Hold

If your turn arrives, you can delay your turn.
You can do this to let one of your allies act before you, or to see what your enemies want to do, and reacto to that.

Interrupting:
If you are holding, you can try to interrupt your enemy's actions. To achieve this, you need to make a contested Roll of Agility & Athletics against the enemy you are trying to interrupt.
If you win, you get to attack before him, otherwise, he attacks first, but you get your turn immediately afterwards

Shaken:
If you get Shaken, wounded or Stunned while on hold, you lose your hold and your turn in this round. You cannot hold while you are Shaken either.