From IIT Bombay Website:-
"As the seats for the SC/ST students are often unfilled because adequate number of students from these categories do not qualify JEE with relaxed norms, a further relaxation of JEE norm is made to select students for a one year Preparatory Course. On passing the course successfully, the students are admitted to the First year of B.Tech./. Integrated programmes against the vacancies for the First year during the year in which the students were selected for the preparatory course"