IST stands for Israel Time - Jerusalem, Tel Aviv, West Jerusalem, Haifa and represents UTC+03:00. Note that IST is used by 2 different zones, so the correct offset depends on the location you mean.
Ambiguous Abbreviation
"IST" has 2 different meanings depending on the region.
UTC+03:00
Current time:
--:--:--UTC+05:30
Current time:
--:--:--