What is it?
Massive Open Online Courses (MOOCs) are classes that scale to massive numbers of participants. The scale either comes through a high level of automation and little teacher involvement or from a distributed nature of a MOOC.
Why is it DIY?
The barriers to entry for both participating in a MOOC or creating one are very low (they are indeed "open"). Technology is the enabler and allows educational processes to scale across organizational and geographic boundaries.