I am new to pistols and want to no what the words ACP means in regards to 45 ACPpistol???????????????????????????????/

Automatic Colt Pistol!

It is a caliber designation. While there are other .45 calibers, such as the .45 LC, and newer .45 GAP, they are not interchangeable!

well now we might as well say that LC is Long Colt and GAP is Glock Auto Pistol!

The term 45 Long Colt is commonly used, and I have used it myself in conversation. In fact, a revolver for that round is labeled simply 45 Colt.

I haven't seen 45 Auto Rimmed on the shelf for years, one of the other 45 variants out there.

I've seen old ammo boxes labeled "45 Long Colt". I believe this came into use when the U.S. Army had two 45's in use. They had handguns chambered for the 45 Colt as well as 45 Schofield. Since the Colt round was slightly longer than the Scholfield, the term "Long Colt" became common.

Makes sense to me. I would prefer to see revolvers labeled as such.

I've seen .45 Colt ammo labeled ".45 LC" so .45 Long Colt is a pretty common term, even if it isn't quite correct!
BTW .45 GAP is Glock Automatic Pistol!