The PTA is a national organization and only official members can call themselves PTAs. There are many independent parent groups that go by a variety of names that we, in general terms, refer to as PTOs. You'll see other PTLs among our community, along with PCCs (Parent Communication Councils) HSAs (Home School Associations) and many, many more.
I have been the treasurer of a PTL for over 8 years and in our case, because it is with St. Mark's Lutheran School, our PTL does stand for Parent Teacher League. As I asked that same question over 8 years ago, I was told that the PTA was a specific organization that was not covered by parochial schools, and that PTL was the choice name.
If that is not the case, then I'd like to know more. Until then, that is what I will stick with. Cheers.
SueMac, have you got the idea that our Forum members are a playful bunch at times? They are also incredibly supportive and helpful.
As far as the name, PTA is the official designation for the Parent Teacher Association. No one can use that name unless they are a member of that group.
Most other unaffiliated parent groups pick their own name. "PTO" is very popular and has some name recognition value among the general population, but as you've seen other versions certainly exist.