Rimfire refers to a type of firearm cartridge design in which the firing pin strikes the rim of the cartridge base to ignite the primer compound. The term "rimfire" comes from the distinctive rim around the base of the cartridge case.

In a rimfire cartridge, the primer is distributed around the entire circumference of the base, creating a rim that contains the primer compound. When the firing pin strikes the rim, it crushes the soft primer compound against the anvil, causing it to ignite and ignite the main propellant charge, firing the bullet.

Rimfire cartridges are generally smaller and less powerful compared to centerfire cartridges, and they are commonly used in small-caliber firearms such as .22 Long Rifle (LR). Rimfire ammunition is widely used for recreational shooting, plinking, small game hunting, and target practice due to its affordability and availability.

It's worth noting that rimfire cartridges are not reloadable, as the primer compound is contained within the rim, making it difficult to replace or reload.