A misnomer- these "mid"terms rarely occur in the middle of a term, and often appear in multiple segments throughout the quarter or semester. aka the name professors tack on to any test between the first week of school and the second to last week of school. (the last week is reserved for "finals"). One of the leading causes for lack of sleep/cramming/coffee overdosage in several college students.
#1 "Dude, it's only the second week of school and I have a midterm coming up"
#2 "Shit man, me too! I have a midterm every week until finals wtf??"