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
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