Overloading is a term used by undergraduates. It means a student is enrolled in more than 1 Unit worth of courses in a single term.
Undergraduates are allowed to register for 1/6 unit worth of credit above the usual 1 unit before an overload fee is charged. This allows students to take an ROTC course or physical education in addition to three other courses.
If an undergraduate entered WPI with no previous credit (transfer or AP), it would be possible to graduate from WPI halfway through the Junior Year at a savings of $42,985 ($46,485 in tuition less $3,500 in overload fees) if one took 4/3 worth of work per term through the normal academic year and two summer sessions. There would also be an estimated savings of $17,610 for all other associated costs. All numbers are accurate for Academic Year 2006.  Although extremely time consuming and difficult, it is possible.