Pawn Structure

Pawn structure is the formation that your Pawns are in. Because Pawns have limited mobility, their structure is very important. The diagram on the left shows a number of different Pawn setups. Here are some of the different types of Pawn formations:

A passed Pawn is one that has no opposing Pawns on it's file or a file next to it. In the above position, Black has a passed Pawn on h6. A protected passed Pawn is the same thing, except the Pawn is protected by another Pawn. White has a protected passed Pawn on f5. Passed Pawns are very valuable because they are much easier to promote.
An isolated Pawn is one where there are no other friendly Pawns on adjacent files. This makes an isolated Pawn hard to defend, so they are usally a weakness. Black has an isolated Pawn on h6.
Backward Pawns have other Pawns on either side of them, but their friends are too far advanced to be able to protect them. If a backward Pawn can be moved forward safely, where it's alongside another friendly Pawn, it loses it's 'backward' status and becomes more valuable. White and Black both have a backward Pawn on the d-file in the above position.
Doubled Pawns are two Pawns, controlled by the same player, that are both on the same file. They cannot protect each other, making them a weakness. Black has doubled Pawns on the a-file.
A Pawn chain is a group of Pawns that protect each other. Pawn chains can be a variety of lengths. In the diagram above, White's Pawns on d3, e4, and f5 create a Pawn chain.

	A passed Pawn is one that has no opposing Pawns on it's file or a file next to it. In the above position, Black has a passed Pawn on h6. A protected passed Pawn is the same thing, except the Pawn is protected by another Pawn. White has a protected passed Pawn on f5. Passed Pawns are very valuable because they are much easier to promote.
	An isolated Pawn is one where there are no other friendly Pawns on adjacent files. This makes an isolated Pawn hard to defend, so they are usally a weakness. Black has an isolated Pawn on h6.
	Backward Pawns have other Pawns on either side of them, but their friends are too far advanced to be able to protect them. If a backward Pawn can be moved forward safely, where it's alongside another friendly Pawn, it loses it's 'backward' status and becomes more valuable. White and Black both have a backward Pawn on the d-file in the above position.
	Doubled Pawns are two Pawns, controlled by the same player, that are both on the same file. They cannot protect each other, making them a weakness. Black has doubled Pawns on the a-file.
	A Pawn chain is a group of Pawns that protect each other. Pawn chains can be a variety of lengths. In the diagram above, White's Pawns on d3, e4, and f5 create a Pawn chain.