common ground

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A foundation for mutual understanding.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun idiomatic A characteristic or interest shared by multiple people or systems; any belief, etc. held in common.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a basis agreed to by all parties for reaching a mutual understanding