a shout or whistle of disapproval, usually made loudly or shrilly at a public event or performance;
e.g. The sportsperson's poor performance earned him catcalls from the fans in the audience.
(noun)
a whistle, call, or a sexually suggestive comment that is directed loudly at someone in a public space, such as by a man to a woman passing by on the street;
e.g. She received a catcall as she passed the men on the street.
(verb)
to whistle, call, or shout loudly, either sexually suggestive comments to women passing by or expressions of disapproval at a public event or performance;
e.g. The began to catcall her when she got out of the car.