What Is an ARP? The Complete Guide to AR Pistols in 2026 Introduction: What Does ARP Mean? If you've been browsing gun stores, firearms forums, or online marketplaces and kept seeing the acronym ARP, you're not alone in wondering what it means. ARP stands for AR Pistol — a compact, AR-platform firearm that meets the federal legal definition of a pistol rather than a rifle or short-barreled rifle (SBR). At first glance, an ARP can look like a shrunken AR-15 rifle, which leads to a lot of c …