Massive: unlimited amount of participants
Open: everybody can attend without regard to origins, degree's or any other distinction
Online: the entire program is meant to be online (course, activities, homework, exam, etc.)
Courses: it is part of an educative program. You can get credits for a grade with those courses
MOOCs are free. They allow people who want to learn and increase their knowledge in any field to be able to do so. They don't have to worry about the price.
There are a lot of resources on the internet for free or for a decent price. The price shouldn't stop you reaching your goals.