D0 == Division 0. Right now all the top teams play in Division 1 athletics, with a bunch of other teams that generally don't get nearly as much money or notoriety but give the top teams some other teams to "beat up on" so to speak (although they do sometimes lose). Division 0 is this idea that the Power 5 (see below) would form their own division.

Right now there are three divisions, and they are based on school size, which is why all the big schools are division 1 but there is a big difference in quality. The idea here is to take the top teams and split off regardless of school size.

P5 == Power 5. These are the five conferences that have almost all the top teams. Big ten, Big 12, the ACC, the Pac-12, and the SEC.

G5 == Group of 5. These are there conferences with the lesser know teams. American, Conference USA, Mid-American, Mountain West, and Sun Belt

Where can I read about this? Are conferences what divisions are subdivided into?

Just google college athletic divisions.

The g5 and p5 are media constructs (not official) designations to help with ratings and assign teams to various invitational competitions like the college football playoffs.

Division 0 (instead of DI, DII(2), or DIII(3) divisions on collegiate sports.

P5 = Power 5 conference, ie ACC, SEC, Pac12, Big12, Big10

G5 = No idea.