"Reserve Officer Training Corps".
ROTC is an arrangement between many US colleges, and various branches of the US military. A student joins the Army or Navy or whatever, and that service pays the student's tuition. In return, the student is trained as an officer along with his or her ordinary education, and serves for a few years in the military after graduation. For the student, it's a chance to work one's way through college without taking on a crushing debt; for the military, it's a supplement to the military academies (Annapolis, West Point, etc.). A lot of students who couldn't afford to go to good schools have benefitted from ROTC programs. My understanding is that graduates of Annapolis, West Point, etc. sometimes aren't too impressed with ROTC officers, but I've spent no time in the military and can't vouch for that.
ROTC students tend to wander around campus in fatigues and boots and butch haircuts.
During the Vietnam era in the US, ROTC was controversial on many campuses. On some, it may be still.