A sobor is a council of bishops and other clerical and lay representatives representing the church in matters of importance. Derived from the Church Slavonic word for "assembly".

Distinct from synod, which is a gathering of only bishops.

In 16th and 17th century Russia, a zemsky sobor was a high council convened by the Tsar.

Also used to mean "cathedral" or "church".

For more information:

http://www.encyclopediaofukraine.com/pages/S/O/Sobor.htm

A photograph of an American sobor: http://www.theocacna.org/sobor.2002.htm