Chibi (ちび, can also be written 禿び) is a Japanese word meaning "short person" or "small child." The word has gained currency amongst fans of manga and anime. Its meaning is of someone or some animal that is small. It can be translated as "little," but is not used the same way as chiisana (tiny, small, little in Japanese).
In English-speaking anime fandom (otaku), the term chibi has mostly been conflated with the term super deformed or it can be used to describe child versions of characters.
See also, Super Deformed, or SD.