proportional representation

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

• noun Representation of all parties in a legislature in proportion to their popular vote.

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

• noun A voting principle aimed at securing a close match between the percentage of votes that groups of candidates (usually political parties) obtain in elections, and the percentage of seats they receive in the elected body.

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

• noun representation of all parties in proportion to their popular vote