RSUMS stands for the Royal Society University Marine Station, which is a research facility located in Oban, Scotland. It was established in 1884 and is the oldest marine station in the United Kingdom. The station provides a range of services to the scientific community, including research, teaching, and public engagement activities. BIOS, the four-letter solution to the crossword, stands for Biological Investigations of the Oceans and Seas, which is one of the main research areas at the station.