The phrase "pop balloons" means to burst or break the balloons by pushing on them or using sharp objects, usually for fun or as a game. Full definition
Once dry, hold the string and pop each balloon with scissors. (idealhome.co.uk)
Instead we just get to pop balloons on eight specific normal courses, which can make tracking someone down an incredible chore even if you can travel in either direction at will. (snackbar-games.com)
The single player gets a nice plane with a gun on each wing as he / she tries to pop the balloons of the team of 3. (mariopartylegacy.com)