Corequisite

From CarlWiki

A corequisite is a course that must be taken either before or concurrently with anoter class. Sometimes, two classes (such as a lecture class and a separate lab) are each a corequisite of the other, in which case they simply have to be taken simultaneously. Other times, it may be preferable for a corequisite to be taken as a prerequisite instead, as with MATH 121: Calculus II being a corequisite to PHYS 113: Newtonian Mechanics.

The phrase "requires concurrent registration in," frequently used in the course catalog, is equivalent to two classes being corequisites of each other, which is how such classes are listed on CarlWiki.