CST stands for Central Standard Time.
CST is six hours behind of UTC (GMT) time, e.g. London, UK. Chicago is one hour behind East Coast Time, e.g. New York City, Miami, Washington DC.
Chicago observes DST. During Daylight Saving Time the time zone is renamed from CST to CDT.
DST (=turn clock 1 hr ahead) begins at 2 a.m. on the second Sunday in March and Standard Time (=turn clock 1 hr back) starts at 2 a.m. on the first Sunday in November.
DST 2010: Sunday, March 14 until Sunday, November 7, 2010
The continental United States of America have 4 time zones:
In addition there are two further zones for:
GMT: Greenwich Mean Time
CST: Central Standard Time (UTC -6 hrs)
CDT: Central Daylight Time (UTC -5 hrs); time span when clocks are advanced 1 hr during the summer months
UTC: Coordinated Universal Time (equals GMT)
DST: Daylight Saving Time in the USA
On August 8, 2005, President Bush signed the Energy Policy Act of 2005, which included changes in Daylight Saving Time, effective March 1, 2007.
Source: Physics Laboratory, U.S. National Institute of Standards & Technology