There are three different forms of betting in the world of poker. These three types are pot-limit, no-limit, and limit. Each form is unique and has its own style of play associated with it. Being able to play each of these different styles is an important skill for any professional poker player but understanding the differences between the three will help to clarify a number of things of the introductory player.
Limit hold'em is when the table sets the amount you can bet. For example, if you are playing at a 2/4 limit table the raise and reraise limit will be two dollars pre-flop and flop and four dollars on the turn and river respectively. There is also often a limit of two or three reraises per betting round.
Pot limit and no-limit are similar but not quite the same. Both forms have much loser restrictions on the amount that a player can bet but in no limit, a player can bet as much as they want whenever they want. For example, if you are first to act pre-flop in no limit, you can push all of your chips in if you want. In pot limit, however, the most that you are allowed to bet at any given time is the amount of money in the pot. In this example, let us say that the pot is six dollars after the flop. In no limit, you would be allowed to be your entire stack but in pot limit, you are allowed to bet a maximum of six dollars.