Any figure added to coats of arms tending to lower the dignity or station of the bearer.  Thus, the baton sinister, denoting illegitimacy, is an abatement.  Abatements have also been called Rebatements.

This is not a good thing to have as they are marks of disgrace attached to arms on account of some dishonourable act of the bearer.

Broken chevrons, and beasts turned towards the sinister, are said by some heraldic circles to have been given as abatements.