In taekwondo, the word chamber means to put one's hands or feet in a preparatory position before performing a movement.
For example, at the conclusion of a Low Block (aka Downward Block) one's fist will be down by one's thigh. But how does the fist get there? Where does it start? To "chamber" for a Low Block, you start by placing the blocking fist at the opposite shoulder. So for example if you're blocking with the right arm, the right fist will start at the left shoulder. In this example, one would say that you chamber for the block by placing your fist at the shoulder.
References
Edit
From http://en.wiktionary.org/wiki/chamber
In martial arts, to prepare an offensive, defensive, or counteroffensive action by drawing a limb or weapon to a position where it may be charged with kinetic energy.
- Bob chambered his fist for a blow, but Sheila struck first.
