Two pawns that occupy the same file.
Two pawns of the same colour on the same file, put there by a capture. These pawns are generally considered to be weak, but they can control valuable squares and create open or half-open files.
Two pawns of the same colour on the same file. These are generally considered a liability.
Two pawns of the same color on the same file as a result of a capture
A pair of pawns of the same color on the same file.
Pawns on the same file, often one obstructing the other, as in the booklet on Pawn mobility.
In chess, doubled pawns are two pawns of the same color residing on the same file. Pawns can become doubled only when one pawn captures onto a file on which another friendly pawn resides. In the diagram, the pawns on the b file and e file are doubled.