Traditionally freshmen first-year courses are 100 series, sophomore second-year course 200 series, junior 300 and
senior 400. So, 101 means a most basic course intended for a first-year freshman.
By the time I was in school, in the 1980s, I think the course numbers at FSU already had five digits. I am not quite sure, but I think, the first digit was the level 1-5 (5 for graduate student courses), the second and third digits indicated the department, and the last two digits indicated the specific course.
Still, back then, if you told someone at FSU you were taking a 101 course, they would have known what you meant.