By definition, "limit" means the greatest or least amount allowed to bet at one time. When playing Limit Poker, one is normally offered different games to choose from dependent upon the limits set.
When a player enters a poker room in a casino setting or online, there will probably be different limit tables to sit down and play in. The limits could be, $2-$4, $3-$6, $4-$8 and so on.
For example, in a $2-$4 limit game, the first and second bet will be limited to $2 and the third and fourth bet will be limited to $4. No more, no less. If a player raises, the raise may only be in increments of the limited amount. Player one is the small blind ($1,) and player two is the big blind ($2). The following player may call $2 or call and raise another $2 making the total amount bet $4. He may not raise more or less than the limit of $2. The next player will fold or call the bet of $4 and may raise it another $2.
After the flop, the betting round is limited to $2 again. When the turn card (4th card) arrives, the betting now is limited to $4 per bet. No more, no less. The river card (5th card) is limited to $4 as well.
Limit poker is also referred to as structured because each bet has a specific structured amount.
Pot Limit Poker
Pot Limit means the limit you may bet is the size of the already existent pot.
For example, take a pot limit game with blinds of $5 and $10. Say there is already $15 in the pot from the blinds when the first player after the blinds is ready to act. The player may call the $10 (the big blind) and make the pot $25. Then raise the total of what is in the pot. Lets say the player does exactly that.
The pot now has a total of the two blinds, $15, the call of $10 and may raise the total $25 making the pot $50. With the pot now being equal to $50, the next player may call the bet of $10 plus the $25 raise from the previous player making it a total call of $35. If he does this, he now has the option to raise $25 (the size of the last raise) or rasie up to the amount of the pot ($85). you can see, the pot may grow rapidly as the deal progresses.
No Limit Poker
No Limit Poker means that there is no limit to the amount of a bet. A player is limited only by the amount of chips in front of him (their stack, or stake).
For example, in a no limit game where the blinds are $5 and $10, the next player may call the $10 big blind or he may "shove in" all his chips as his bet. This is also referred to as "moving all in" or "going all in". This player has the option to bet any amount between the mandatory $10 blind bet and his total stack. This is true at any time during any hand when it is your turn to act.