All the opportunities you get to score a goal. Most users believe that the maximum amount of opportunities is set to 14 per match.
This match however (48729175) ended in 13-2, so the 14 opportunities must be wrong. It is believed there is a maximum of 10 normal chances per game plus an indefinite number (with a decreasing chance for each following one) SE's per game. This match for example had 6 SE's: (50627803)