# Probability of an event is p, average attempt until p happens?

Say there is a chance p of an event happening each attempt. How many attempts (on average) would it take for this event to occur once?

For example, say the event is a racquetball player hitting a killshot, which he has a 20% chance of doing every shot.

On average, how many shots until he hits a killshot? I remember learning this, but forgot the name.