The sound of disgust coming from a crowd at a sporting event after something they didn't like happens.
The sports announcers reported, "That questionable call by the officials brings out the 'Boo Birds'."
by ChrisDoc November 10, 2009
2 more definitions
Home team fans at a sporting event who boos one or more members of the home team because of the team playing bad.
The boo birds are out tonight.
by stanley2toronto September 28, 2011