home plate

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

• noun A base, usually consisting of a hard rubber slab, at one of the corners of a diamond at which a batter stands when hitting and which a base runner must finally touch in order to score.

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

• noun baseball A flat, pentagonal, rubber object placed at the center of the batter's box, which is used as a basis for judging pitched strikes and balls, and the touching of which by a runner advancing from or past third base scores a run.

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

• noun (baseball) base consisting of a rubber slab where the batter stands; it must be touched by a base runner in order to score