I. boo 1 /buː/ BrE AmE verb [intransitive and transitive]
to shout ‘boo’ to show that you do not like a person, performance, idea etc:
Some of the audience started booing.
She was booed off stage (=they shouted ‘boo’ until she left the stage) .
II. boo 2 BrE AmE interjection
[ Date: 1800-1900 ; Origin: Natural sound ]
1 . a noise made by people who do not like a person, performance, idea etc
2 . a word you shout suddenly to someone as a joke in order to frighten them
3 . wouldn’t say boo to a goose an expression used to describe a shy quiet person