A "Poison Pawn" is a pawn that often seems like any other pawn left open to capture for free, but when captured, causes problems for the player who captured it. Quite often "Poison Pawns" are left as bait.
Example 1: He captured what he thought was a free pawn, but it was a "Poison Pawn". In doing so, he left his King open and was checkmated.
Example 2: He captured the pawn on square e5 with his Knight, but doing so his left his Queen open to be taken by a Bishop.(A much less valuable piece.)
He took "The Bait"