Distinguish between Greenwich mean time and Indian Standard time.
Greenwich mean time can be defined as the mean solar time at the greenwich meridian, adopted as the standard time in a zone that includes the british Isles.
Indian standard time can be defined as the time observed throughout india and srilanka with a time offset of UTC+05:30.
and the difference between GMT and IST is it varies in time duration that is IST is 5 hours and 30 minutes ahead of GMT.