Definition and background:
A symbol that looks like an archer's bow (also called curved brackets) that are used to connect two or more different staves in a musical score into a system. The brace will typically provide a visual connection between dependent parts (i.e. two piano staves) into a system. This should not be confused with the bracket that provides a visual connection between independent parts into a system. Also [Eng.] brace; [Fr.] accolade; [Ger.] Klammer; [It.] accolada.
For more information on the music term "Brace" check out these other resources:
Wikipedia - Glossary of Musical Terminology
Virginia Tech Multimedia Music Dictionary
ORB -- Medieval Music Glossary