Def. 1 A pawn is passed if no opponent's pawn could block or capture it, that is, if no opposing pawn sits in the same or either adjacent file. In the illustration at the right, white's 3 knight and rook pawns at squares a6, b5, and g4 are the only passed pawns. Def. 2 Two pawns are connected if their files are adjacent. The idea here is that connected pawns can protect one another, at least in the future, leaving the pieces free to perform more important duties. In the figure at the right, all pawns of both colors are connected, except white's pawn at g4.

Def. 3	A pawn is isolated if it is not connected to another pawn. In the figure above, the only isolated pawn is white's pawn at g4.
Def. 4	Two pawns are doubled if they occupy the same file. In the figure above, only black's two king pawns are doubled. In the rare event that 3 pawns occupy the same file, they may be called doubled or tripled.

Def. 5	You have a one pawn advantage (or n pawn advantage) if you have one (or respectively, n) more pawn(s) than your opponent. In the figure above, white has a one-pawn advantage.
Def. 6	You have a one pawn disadvantage (or n pawn disadvantage) if you have one (or respectively, n) fewer pawn(s) than your opponent. In the figure above, black has a one-pawn disadvantage.(or respectively, n) more pawn(s) than your opponent.
Def. 7	A pawn is backward if there is no friendly pawn closer to the starting position in either adjacent file. Backward pawns are difficult to avoid: white's pawn at e2 is backward.

The idea is this: be constantly aware of what your position would look like if the pieces were exchanged, one for one, until only the pawn structure remained. When you perceive that you have the better pawn structure, attempt to trade off all pieces to magnify and solidify that advantage. If you perceive that your opponent has the better pawn structure, avoid exchanging until you have used your pieces to gain the better pawn structure.