E.S.T. stands for Eastern Standard Time, which is a time zone that is 5 hours behind Coordinated Universal Time (UTC-5). It is primarily observed in the eastern part of the United States and parts of Canada. E.S.T. is used during the fall and winter months, while Eastern Daylight Time (EDT) is observed in the spring and summer when clocks are set forward by one hour. E.S.T. is important for scheduling events, transportation, and communication across regions. Major cities like New York, Washington D.C., and Toronto operate on E.S.T., making it a key time zone for business and travel in North America.