What is it called when opposite colored pawns up against each other? When a white pawn and a black pawn are touching on a file, what is it called?
With the exception of Hans Kmoch's attempt to give it a name, which never caught on (I have never seen anyone else use it anywhere), they really do not have a name that I have even seen.

I probably have seen this referred to mostly as "two opposing pawns", but that is really just English rather than a specific chess term.