blank verse

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

• noun Unrhymed verse having a regular meter, most commonly iambic pentameter.

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

• noun A poetic form with regular meter, particularly iambic pentameter, but no fixed rhyme scheme.

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

• noun unrhymed verse (usually in iambic pentameter)