daylight time
noun
Definitions
The practice in some places of adjusting clocks forward in the spring and back in the fall, usually by one hour, so that the adjustment causes the time to coincide with the greatest period of illumination by the sun over the course of the day.
Example: 2005: answers.firstgov.gov -- Daylight Saving Time is a change in the standard time of each time zone. ... The American law by which we turn our clock forward in the spring and back in the fall is known as the Uniform Time Act of 1966. The law does not require that anyone observe Daylight Saving Time; all the law requires is that if we are going to observe Daylight Saving Time, it must be done uniformly. http//answers.firstgov.gov/cgi-bin/gsa_ict.cfg/php/enduser/std_adp.php?p_faqid=6880