daylight-saving time

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

• noun Time during which clocks are set one hour or more ahead of standard time to provide more daylight at the end of the working day during late spring, summer, and early fall.

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

• noun time during which clocks are set one hour ahead of local standard time; widely adopted during summer to provide extra daylight in the evenings