3 units: Refers to the amount of credit a college course is worth. Each college or university has its own system for determining how many credits a class is worth, but generally speaking, one credit is equivalent to one hour of lecture time per week for a semester or quarter.
Requirements vary by college: Different colleges and universities have different distribution requirements for social science courses. Some schools may require students to take a certain number of credits in social sciences, while others may allow students to choose from a wider range of courses.
In addition to the above, some schools may also include courses in the humanities and arts as part of their social science requirements.