What is the "p" in CpG?

[David Neece]

OK, here's a question that just might make you recant the "no such thing as a 
stupid question" postulate...

What does the "p" in CpG (as in CpG island/repeat) stand for?

I've been reading several interesting articles about CpG islands and genome 
evolution, but none (nor any text books I've consulted) offer an expanation.  
Am I missing something obvious?

Dave Neece
University of Illinois