Boo

Boo is a term with multiple senses in English. It can function as an interjection to express disapproval or to frighten, as a term of endearment for a romantic partner, or as a proper noun in various names and works of fiction.

As an interjection, boo conveys contempt or dissatisfaction and is commonly used by audiences to hiss or jeer at performers. The expression has a long history in English-speaking cultures, with booing events documented since at least the 18th century.

As slang or an affectionate nickname, “boo” designates a boyfriend, girlfriend, or romantic partner. Its rise in popular usage has been linked to music, social media, and casual speech; its exact origins are uncertain and it remains informal and regionally diverse.

In popular culture, Boo is the name of ghostly characters in Nintendo’s Mario video game series. Boos are shy white ghosts that float and often cover their faces; King Boo appears as a boss character in several titles. The term also appears in various other media and consumer products as a character name or title.

Boo is also the name of a programming language for the .NET platform, with Python-inspired syntax, designed to run on the Common Language Runtime. This usage reflects one of several distinct meanings of the word, separate from its interjectional or affectionate uses.