Brace:

When you enter the 'brace' command to brace your character, your character will no longer move. It can still attack adjoining spaces. Bracing can be useful to hold a location.

When you are braced, you lose your dex bonus and incur a 2 point ac penalty beyond that (if you have a negative dex bonus, you may in fact come out ahead. You also only get 20% of the normal experience for killing creatures, and incurs a 4 point wc (to hit) penalty.
