It sounds like you are referencing as a chess piece.
Could you provide the context (e.g., "ftex moves like a ___")? I can give you the exact definition from the specific fairy chess problem you're looking at.
However, you are likely thinking of or a specific chess variant. Here is the most probable match:
In standard chess notation, is not a valid piece abbreviation (the standard abbreviations are K, Q, R, B, N, P).