Mike wrote:
I've read the term ground loop in a lot of articles and accident reports but
what exactly is a ground loop?

Go to AvWeb.
Under COLUMNS, select the index for John Deakins columns.
Look for the article on Edwards AFB Flight Testing.
Deakins gave instruction in a T-6 Texan (the original) to test pilot
candidates.
At the end of the lesson, he describes how he set them up for a ground
loop.