Def1) Sex. It can be anything from handjobs/fingering to oral to full penetrative sex. Must be indoors (hence the "room"). May also involve some kind of competitive game or specific goal, but this is not neccesary to qualify as roomsport.
Def2) Random exclamation of happiness or excitement, possibly about the prospect of roomsport itself.
The word "Roomsport" is believed to have originated in either southwestern Ontario and Vancouver, British Columbia.
John- "What did you and Jessica do last night?"
Ed- "I bet I can last longer than you"
Steve- "No fucking way"
Ed- "Fine, roomsport"
Fred- "I'm going to make her squirt, roomsport tonight"
John- "Why are you so excited?"
Jun- "My parents are buying me a BMW"
John- "You rich mother fucker"