UTC stands for Coordinated Universal Time. In 1972, it replaced GMT, or Greenwich Mean Time, as the key reference time scale for various regions. EST is five hours behind UTC, while EDT is four hours behind. EDT refers to the United States Daylight Saving Time. In 2014, EDT was from March 9 to November 2.
The United States has six time zones: Eastern, Pacific, Alaska, Hawaiian-Aleutian, Mountain and Central Time. All of the regions are subdivided into standard and daylight time zones.Learn more about Time Zones