Limp

Before the flop, the action comes to you and you have three choices: fold, raise, or just match the big blind. When you choose that last option and only call the big blind rather than raising, you've limped in. You're paying the cheapest price to see the flop without showing any strength, and if others have already done the same it's called an over-limp (limping behind).

This comes up most often in loose, friendly games where several players want to see a cheap flop. If one player limps and you also just call, the pot can fill up with limpers, which usually means a lot of people seeing the flop for very little. It's different from a raise because you're not building the pot or pressuring anyone to fold, and it's different from a fold because you're still in the hand.

For beginners, limping is usually a habit worth dropping. Open-limping (being the first one in for just a call) gives away the chance to win the blinds right away and lets players behind you in cheaply, often out of position. A simpler, stronger default with hands you like is to raise or fold rather than limp, saving the limp for specific spots once you're more comfortable. With practice chips it's a great thing to experiment with so you can feel the difference yourself.