Mathematics

Numeral system

Numerator

Numerical analysis

Numerical digit

Numerical integration

Numerical linear algebra

Numerical methods for partial differential equations

O

O (letter)

Obelus

Obelus (÷): symbol, history, forms and uses

Obtuse angle

OCaml

OCaml (Objective Caml)

Octadecagon

Octagon

Octagon: definition, properties, history and practical uses

Octahedron

Octal

Octal numeral system (base 8)

Odd number

Odds

Omega

Omega (Greek letter Ω, ω)

Omicron

On-Line Encyclopedia of Integer Sequences

On-Line Encyclopedia of Integer Sequences (OEIS)

One-way function

Ones' complement

One's complement (bitwise inversion in binary arithmetic)

OpenOffice Math

OpenOffice Math — Formula editor for the OpenOffice office suite

Operand

Operand (mathematics): definition, types, and usage

Operation (mathematics)

Opposite

Opposite number

Opposite number (additive inverse)

Order of magnitude

Order of operations

Order theory

Order theory: partial orders, lattices, and applications

Ordered pair

Orders of magnitude (time)

Orders of Magnitude of Time

Ordinal number

Ordinary differential equation

Ordinary differential equation (ODE)

Ordinary least squares

Ordinary Least Squares (OLS): method, properties, and applications

Orientability

Orientability in topology and geometry

Orthographic projection

Orthonormality

Orthonormality in Inner Product Spaces

Oscillation

Ounce

P versus NP problem

P versus NP: the central question in computational complexity

An overview of the P versus NP problem: definitions, intuitive examples, historical milestones, consequences of either outcome, and current research directions in complexity theory

Padding (cryptography)

Palindrome

Palindrome: definition, types, history and examples

A palindrome is a sequence—word, sentence, or number—that reads the same backward and forward. This article explains forms, rules, history, examples, and cultural and technical use

Palm (unit)

Palm (unit of length)

Parabola

Parallel

Parallel (geometry)

Parallel postulate

Parallel postulate (Euclid's fifth postulate)

The parallel postulate: Euclid's fifth axiom that distinguishes Euclidean geometry. Covers its statement and equivalent forms, history of attempts to prove it, development of non‑E