Short for "proposition bet." Examples include "LeBron over 27.5 points," "first team to score," or "will there be overtime?" Player props in particular often have softer lines than main markets, making them a fertile area for sharp bettors — which is also why books limit prop winners aggressively.
Markets & bet types
Prop bet
A bet on something other than the final outcome — player stats, game events, etc.
Example
Nikola Jokić assists O/U 8.5 (-115 over / -105 under).