Definition of pot
The term "pot" refers to the pool of money. The money that players play for in each poker hand is called a pot. In online poker rooms, when you want to use the shortcuts to make your bets, you will see "50% pot", "75% pot", "pot". It's a very common way of thinking to orient your bet size to the size of the pot. Each pot will play differently depending on its size. A bluff would be meaningless if you bet 5% of the pot size to bluff. When playing a poker hand, always keep the pot size in mind.
Some general information on the different pot sizes
People will bluff more often in big pots. Also, the hand that wins a big pot is often stronger than the hand that wins a small pot. If there are several players competing for the same pot, you will need to have a very strong hand to be part of the battle. Generally, when players overbet the pot, they will be polarized; some of the time they will have a very strong hand and some of the time they will have a bluff.