Definition of walk
A walk in poker is something that can only happen to you when you are in the big blind. A walk is when all the players before you have folded and therefore you win the blinds without even having to play the hand. Since all the players have folded before you, you don't have to show your hand, you just collect the pot.
You will probably get more walk in tournaments than in cash games. For example, if you have a very aggressive tournament image and you are the table leader in chips, you will likely get a lot of walks. Players, without a hand, will not dare steal your blind. They will think that you are very aggressive and will not let you get away with it. Also, since you have a big stack, you are more likely to call. This is a good reputation to have in this situation because in reality, you won't always be able to defend your precious blinds in tournaments. A walk is always a good thing when you're in the big blind (except when you have a monster of course).