Nigger is a racist insult against black people. It can also be referred to as the "hard R", due to the word ending in 'er' instead of 'a', like the word with a similar meaning - "nigga". Like the word "nigga", it can be used in pop culture slang. However, it is mainly used by those who believe that white people are better than everybody else.
The word came from a slang pronunciation of "negro", which is the word for the color black and for black people in Spanish and Portuguese. Before 1865, most black people in the United States were slaves. During this time, the word "nigger" usually meant a slave. Writers such as Joseph Conrad, Mark Twain, and Charles Dickens used it.
Today, the word is an offensive racial slur in English, and is often thought as hate speech. "Nigger" has become so offensive to say that most people do not use the word; instead, they call it the "N-word".