Yep, the question is not really all too clear.
"1911" refers to a style of handgun, designed by John Browning for the the U.S. Govt sidearm trials for the armed forces. It became the standard Govt Issue sidearm and remained so until 1985. These days, "1911" pistols are made not only by dozens of different manufacturers, but it also comes in many different chamberings. Though .45 ACP (same as .45 Auto) is the standard and most common chambering, it's also been known to shoot 9mm, .38 Super, .40 S&W, 10mm, .45 Super, .460 Rowland, .50GI and even .22LR with a conversion slide, barrel, spring and magazine. Are there any I forgot?
".45 ACP" is a chambering common to many different handguns... mostly semi-auto pistols, but also a few revolvers. Outside of the "1911" style, .45's can also be found by S&W, Ruger, HK, Glock, Springfield XD, and many, many more.
The reason the 1911-style pistol is so popular these days is due to many reasons. It's quite familiar to most folks, since it's been around for so long. The design gives it very good trigger, though it does vary from pistol to pistol. Because so many different companies make it, there is also a huge aftermarket support for parts and holsters and accessories. It's design is very much loved and the platform can be made to be quite accurate. They are splattered all over the magazine covers. Add all that up and toss in the fact that some of the most well-known and historic manufacturers in the world's history are making them and it a slam-dunk that it's going to be a very, very popular style of handgun.