"УИС" stand for Улсын Их Сургууль (Ulsyn Ikh Surguuly), which translates to "State University".
When combined with "Монгол" (Mongolia), it forms МУИС (Монгол Улсын Их Сургууль), the National University of Mongolia—the country's oldest and primary public university, located in the Ulaanbaatar.
