Definition of pot bet
A pot bet is a bet equal to the size of the pot. If on the flop there are 10??? in the pot and a player bets 10???, he is said to be making a pot bet. This is not a common bet in poker. It is not uncommon either, but it is far from the most common bet. Usually, on the flop, players will bet 33% pot, 50% pot or 75% pot. When they make a pot bet, it is because they have a specific reason, for example, to discourage a player from running a draw.
If you make a pot bet, have a good one
Usually, we want to give our opponent a tough decision. If we bet 50% pot, we often give him a hard decision with a good part of his range. If we pot bet, for him the decision will be easier. He won't pay with his low draws and when he has a monster (a very strong hand), you will simply have lost more money with your larger bet. There are still good reasons to pot bet, but you have to be careful. For example, if you're playing against a player who loves to pay pot bets with simple draws, don't hesitate to bet big.