My course says that it is "2 units." What does "unit" mean?

A unit (or unit of credit) represents the amount of work in a course.  Each unit represents approximately 30-45 hours of work by the student, including both class attendance and preparation. So if you are taking a 2-unit class in the summer, you can expect the total amount of work in the class to take you 60-90 hours/term. See for more information.