Metagaming is a pretty generic term, but applied to role playing games it refers to having your character act on knowledge they do not have.

Let's say that your character encounters a cop in a modern day adventure. You, the player, are a police officer, and have a great deal of knowledge about the rules and regulations that in-game cop will follow. Your character is a farmer from the country, and knows only the corrupt small town police in his own town.

You could play that encounter two ways.

Your character could blunder through the encounter based on his own knowledge, generally making things worse with every action. Maybe he offers a small bribe, because that's what worked back home. Before too long he's in front of a judge and facing jail time.

Or you could use your own knowledge to have your character do everything exactly right and breeze through the encounter. That's metagaming.

Here's another example. Often, in role playing games, the characters split up. One half of the group goes to accomplish one task, the other half goes to accomplish another.

Let's say that the thief and the wizard go to perform a spell at the evil lich's power focus that will destroy him forever. But, unless the liche's magic gem is destroyed before that, the feedback will destroy the entire mountain the group is in. So the fighters head for the gem to destroy it. The wizard is to wait one hour and then perform the ritual.

Each half of the group is completely separated, but the players are all at the same table. So the players hear what is happening with the other group. The fighters are defeated and imprisoned, and the gem is not destroyed.

Does the wizard's player perform the ritual as scheduled? The chances are good that the player will come up with some reason not to perform it, even though the character would absolutely perform the ritual (and thus destroy themselves).

When we metagame in an RPG, it's usually to get an advantage for our character. That's usually because the player is oriented to "winning" the game.

I see this most often with players who started RPGs early in life, say in their teens. At that age, winning is very important!

With players who start playing as adults, metagaming is less prevalent, in my experience. Those gamers are more interested in having fun with the game, even if that means their characters do something extremely bad.

Some people see metagaming as a problem that needs to be solved. In reality, it's just one way that some players have fun with the game. Know your group, and if metagaming is what drives them, then play games where that's an expected part of the game. And stay far away from games like Call of Cthulhu, where the entire fun of the game is seeing how creatively your character can go insane.

And remember, whether you metagame or not, definitely Game!