What do the letters AR stand for in the AR-15 rifle?
The letters AR in the AR-15 rifle stand for Armalite Rifle, which is the name of the original manufacturer of the firearm. The AR-15 was first designed by Eugene Stoner in the 1950s for the company Armalite, which was later sold to Colt's Manufacturing Company in the 1960s. The AR-15 is a popular semi-automatic rifle that is used for a variety of purposes, including hunting, sport shooting, and self-defense.
What are other popular rifles of the same type?
Other popular rifles similar to the AR-15 include:

M4 Carbine - A shortened version of the M16A2 assault rifle used by the United States military. It features a shorter barrel length than the AR-15 but retains most of its functionality.

M16A2 Assault Rifle - The standard issue rifle of the US Military from the late 1980s until it was replaced by the M4 in the early 2000s. It features a longer barrel than the AR-15 and an automatic firing mode.

Ruger Mini-14 - A civilian variant of the M14 battle rifle produced by Sturm, Ruger & Co. It uses .223 Remington cartridges and has a smaller magazine capacity compared to the AR-15.

Sig Sauer MCX Virtus - A modular rifle platform developed by Sig Sauer that allows users to easily switch out various components such as the handguard, stock, and trigger group. It utilizes a gas-piston operating system instead of a gas tube like the AR-15.

These rifles share many design elements with the AR-15 and offer shooters additional options when choosing a modern sporting rifle. Their specific characteristics may appeal more to certain groups depending on factors like intended use, personal preference, and local regulations.