The term 'mains' refers to the second stage of the UPSC examination process, which follows the preliminary round. The Mains exam comprises multiple written papers, testing a candidate's knowledge, analytical ability, and proficiency in language. Successful candidates from the Prelims move on to the Mains, which includes both General Studies and optional subjects. Performance in the Mains significantly influences the final ranking, as it assesses candidates in a more comprehensive manner compared to the screening nature of the Prelims.