A semi-automatic pistol is a type of pistol that is semiautomatic, meaning it uses the energy of the fired cartridge to cycle the action of the firearm and advance the next available cartridge into position for firing. One cartridge is fired each time the trigger of a semi-automatic pistol is pulled; the pistol's "disconnector" ensures this behavior.
The energy from a fired cartridge allows the next cartridge to move into position for firing in a semi-automatic pistol.