A whoop is a noise you make when you're celebrating something exciting. Just listen to the whoops and cheers from the crowd when your school's basketball team unexpectedly wins the championship!
The joyful hooting of friends hearing your good news, the cheers of fans celebrating a bowler's strike, or the call of a cowboy urging a horse forward — these are all whoops. You can use this word as a verb too, as when you whoop with joy or laughter, or in the colloquial phrase whoop it up, meaning "have a blast." Whoop sometimes also used for the distinctive cough of someone suffering from pertussis, also known as whooping cough.