Nickname

A nickname is a substitute for the proper name of a familiar person, place, or thing, for affection or ridicule.

The term hypocoristic is used to refer to a nickname of affection between those in love or with a close emotional bond, compared with a term of endearment. The term diminutive name refers to nicknames that convey smallness, hence something regarded with affection or familiarity (e.g., referring to children), or contempt.