Relative Pin

A relative pin in chess is when a piece is pinned, but it can legally move. However, it is a bad idea because moving the piece would expose a more valuable piece behind it to capture. This differs from an Absolute Pin, where moving the piece would illegally expose the king to check. Let's take a look at an example:

How should Black play here? Well, White's knight and queen are nicely aligned on the same diagonal asking for trouble! 1...Bg4!

The knight is pinning to the queen - it can move, but that would expose White's queen to our bishop's attack! White has no choice, but to try and defend the knight with 2.Kg2 We now add one more attacker to the party: 2...Ne5!

White has run out of defenders - Black is going to capture the knight on the next move and win the game.