GMT and IST refer to two different time standards used in different regions of the world.
GMT: GMT stands for Greenwich Mean Time. It is a time standard based on the location of the Royal Observatory in Greenwich, London, United Kingdom. GMT is used as a reference point for timekeeping worldwide. It does not observe daylight saving time, so it remains the same throughout the year.
IST: IST stands for Indian Standard Time. It is the time standard used in India. IST is UTC+5:30, which means it is 5 hours and 30 minutes ahead of GMT. IST is maintained throughout the year and does not observe daylight saving time.
In summary, the main difference between GMT and IST is the geographical region in which they are used and the time offset from Coordinated Universal Time (UTC). GMT is a reference time standard based in Greenwich, London, while IST is the standard time used in India and is 5 hours and 30 minutes ahead of GMT.