Communication

Radio (wireless communication and broadcasting) Radio Radio is the transmission and reception of information by electromagnetic waves. It enables broadcasting, two-way communication, navigation and remote control across many frequency…

Radio frequency: overview, propagation, bands, history and applications Radio frequency Radio frequency (RF) describes the portion of the electromagnetic spectrum used for wireless transmission. This article explains RF ranges, propagation modes, historical developmen…

Railway Gazette International — global business journal for the rail industry Railway Gazette International Monthly business journal in English covering mainline rail, metro, light rail and tram sectors worldwide: technical, commercial and regional reporting, news and analysis for indust…

Railway semaphore signal A mechanical fixed signal used on railways that conveys movement authority by the angle of a pivoted arm; historically widespread and largely replaced by colour light signals.

Railway signal: function, types, history and modern systems Railway signal Overview of railway signals: what they are, how they communicate movement and speed to train crews, main types (semaphore, colour-light, in-cab), historical development, and modern…

Rajasthani language Rajasthani is a group of Indo-Aryan varieties spoken across Rajasthan and neighbouring areas; it includes several regional dialects, a rich oral literature, and ongoing debates abo…

Reading: processes, types, history, and practical uses Reading Reading is the cognitive process of extracting meaning from written or printed language. This article explains how reading works, its history, common forms and uses, and techniques…

Real Time Streaming Protocol (RTSP) Real Time Streaming Protocol RTSP is an application-level network control protocol for streaming media that provides VCR-style control over media servers. It was defined by the IETF in 1998 and commonly used w…

Rebus: visual wordplay using pictures, letters, numbers and symbols Rebus A rebus uses images, letters, numbers or symbols to represent words or syllables by sound or appearance. Used in puzzles, signage, logos and language learning, it relies on phoneti…

Receipt: proof of a transaction or delivery Receipt A receipt documents that goods, services or payments were received. It appears as paper or electronic records and is used for returns, accounting, warranties, and tax purposes.

Received Pronunciation — the traditional prestige accent of British English Received Pronunciation Received Pronunciation (RP) is a historically prestigious accent of British English associated with education, broadcasting and dictionaries. This article covers its features, hist…

Receiver (communications) Receiver Device that captures electromagnetic or electrical signals and converts, amplifies, and processes them for radio, TV, radar, satellite and data communications.

Recognition signal A recognition signal is any sign, code or molecular feature used to identify a person, vehicle, object or biological partner. It spans visual, audio, electronic and chemical method…

Red box (payphone phreaking device) Red box A red box is a small device used by phone phreaks to mimic payphone coin deposit tones and obtain free calls; once common in the 20th century, it became obsolete as telephone syste…

Red ribbon (symbol of HIV/AIDS awareness) Red ribbon Looped red ribbon widely used as a symbol of awareness, solidarity, and support for people living with HIV and AIDS; origins, meanings, uses, and notable distinctions.

Redundancy (information, computing, and engineering) Redundancy Redundancy is the inclusion of extra information, elements, or capacity beyond what is strictly necessary. It appears in communication, storage, databases, engineering and natural…

Reflection (wave phenomena) Reflection Reflection is the redirection of waves at a boundary so energy returns into the originating medium; covers principles, types (specular, diffuse, total internal), examples, and comm…

Register (linguistics) Register in linguistics describes language varieties tied to social situation, purpose, and participants—shifting vocabulary, grammar, and tone across formal, informal, occupationa…

Relay (electrical switch) Relay A relay is an electrically operated switch that uses a coil or electronic circuit to open or close contacts, enabling control, isolation and remote switching in telegraphy, vehicle…

Reverberation: acoustic persistence of sound in enclosed spaces Reverberation Reverberation is the persistence and decay of sound in an environment after the source stops. It shapes perception, affects clarity, and is measured, controlled, and used in archit…

Revised Romanization of Korean The official South Korean system (since 2000) for rendering Korean Hangul in the Latin alphabet. It replaces older systems, avoids diacritics, and standardizes place names and sign…

Rhetorical question A rhetorical question is a question asked to make a point rather than to receive information; used in speech and writing for emphasis, persuasion, engagement, or irony.

Rhetorical Triangle: Ethos, Pathos, and Logos in Persuasion Rhetorical Triangle Overview of the rhetorical triangle—ethos, pathos, and logos—its origins, components, uses in speech and writing, and practical guidance for balancing appeals ethically and effecti…

Riddle: types, history, and methods of solving Riddle A riddle is a concise puzzle posed as a question or statement that requires ingenuity or lateral thought to solve. Covers forms, history, solving methods, uses in culture and notab…

Ring (diacritic) Small circular diacritic placed above or below letters in various Latin alphabets and in phonetic notation; marks distinct letters, historical vowels, or phonetic voicelessness.

RM4SCC (Royal Mail 4-State Customer Code) RM4SCC RM4SCC is a high-speed 4-state barcode developed by Royal Mail to encode UK postcodes and routing data; it uses groups of vertical bars, start/stop markers and a checksum and has i…

Roar: biological sound, function, and cultural meanings Roar A roar is a loud, low-frequency vocalization produced by many large mammals and used metaphorically by humans. This article covers its anatomy, acoustics, functions, social role, c…

Romanization of Bulgarian: the Streamlined System and related practices Romanization of Bulgarian Overview of the Streamlined System for Romanizing Bulgarian Cyrillic, its purpose, features, history, common uses and how it differs from other transliteration approaches.

Romanization of Ukrainian How the Ukrainian language is represented with Latin letters: methods, systems, examples, uses, and challenges in transliteration and transcription.

Royal Thai General System of Transcription (RTGS) Royal Thai General System of Transcription The official Thai-to-Latin romanization system that uses only the 26 basic Latin letters. Widely used on signs and official documents; it omits tones and vowel length, producing so…

Russian language Russian is an East Slavic language native to Russia and widely used across Eurasia. This article outlines its characteristics, history, writing system, distribution, and cultural r…

Rusyn language: an East Slavic tongue of Central Europe Rusyn language Rusyn is an East Slavic language (also called Ruthene) spoken by communities across Central Europe. It has several local varieties, varying orthographies, and differing legal statu…

RÚV — Iceland's National Public-Service Broadcaster RÚV RÚV (Ríkisútvarpið) is Iceland's state public-service broadcaster, providing television, radio and online services in Icelandic with a remit to inform, educate and preserve nationa…

SA (abbreviation) SA Overview of the abbreviation SA, its common meanings across languages and fields, historical notes, and how capitalization or punctuation changes its sense.

Samekh: The Semitic 15th letter representing /s/ and ancestor of Greek Xi Samekh Samekh, the 15th letter of Semitic alphabets (Phoenician, Hebrew, Aramaic), represents /s/ and has the gematria value 60. Its Phoenician form is the ancestor of Greek Xi (Ξ). Explo…

San (ancient Greek letter) San (letter) San (Ϻ, ϻ) is an archaic Greek letter used in some regional alphabets for an /s/ sound. It resembled Mu in shape, fell out of use by the 6th century BC, and survives only in inscri…

Sardinian language: overview, dialects, history and contemporary status Sardinian language Sardinian (Sardu, Limba sarda) is a Romance language native to Sardinia. It has several dialects, a regional standard, and a distinctive linguistic history with strong Latin conser…

Scanlation: fan-driven scanning and translation of comics Scanlation Scanlation refers to fan-made scanning, translation and distribution of comics (often manga) not officially localized. It covers methods, community practice, history and legal/ethi…

Scots: the Germanic language of Lowland Scotland and Ulster Scots Scots is a West Germanic language variety spoken in Lowland Scotland and parts of Ulster. Distinct from Scottish English and Gaelic, it has its own history, varieties, literature a…

Scottish English (Scottish Standard English) Scottish English Variety of English used in Scotland that reflects Scots influence; distinct in pronunciation, grammar and vocabulary and used across education, media and everyday speech.

Scottish Gaelic (Gàidhlig) Scottish Gaelic language Scottish Gaelic (Gàidhlig) is a Goidelic Celtic language of Scotland, related to Irish and Manx. It has distinct dialects, a written tradition in Latin script, and ongoing cultural…

Scottish language (Scots, Scottish Gaelic and Scottish English) Scottish language Overview of the term 'Scottish language', its main varieties (Scots, Scottish Gaelic, Scottish English), history, characteristics, cultural role and modern status.

Seal (device): marks, instruments and their uses Seal (device) A seal is a physical mark or the device that makes it, used to authenticate documents, packages and objects; includes wax impressions, signet rings, embossers and modern seals.

Searching Overview of searching: meanings, methods, algorithms, applications, and distinctions across computing, information retrieval, and everyday contexts.

Second person: grammatical role, forms, and narrative use Second person Second person denotes the addressee in grammar and speech; it includes pronouns and verb forms (you, thou, tú), distinguishes singular/plural and formal/informal, and figures promi…

Section sign (§): typographic symbol used in legal citations and texts Section sign The section sign (§) is a typographic symbol denoting a section or subdivision of a document or statute. Common in legal citations, it is encoded in Unicode and appears as § in HTM…

Secure channel (cryptography) Secure channel A secure channel is a communications method that protects data from eavesdropping, tampering, and impersonation. This article explains properties, mechanisms, examples, and practic…

Secure Shell (SSH): secure remote login and data-transfer protocol Secure Shell Secure Shell (SSH) is a cryptographic network protocol for secure remote login, command execution and file transfer between computers over an unsecured network.