Centerfire
A cartridge that fires from a replaceable primer seated in a central pocket in the case head. The standard ignition system for precision rifle rounds.
In a centerfire case the primer sits in its own pocket at the center of the head, struck by the firing pin to ignite the powder charge. Because that primer is a separate, replaceable component, the empty brass can be cleaned, resized, and loaded again, which is the whole foundation of handloading for precision.
This is the dividing line that matters for long range: every cartridge worth pushing to its ceiling, from the .223 Remington up through the .338 Lapua Magnum, is centerfire. The contrast is rimfire, where the priming compound lives in the rim and the case is spent for good after one shot.