fore-and-aft sail

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

• noun A sail set more or less parallel to the keel of a vessel, attached to a mast or stay at its foremost edge and designed to catch the wind on either surface.

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

• noun any sail not set on a yard and whose normal position is in a fore-and-aft direction