What is "touch hole"

n. A small hole through which the propellant charge of a cannon or muzzleloading gun is ignited.

A touch hole, also called a vent, is a small hole near the breech of a cannon or muzzleloading gun through which the propellant charge is ignited. In small arms, the flash from a charge of priming held in the flash pan is enough to ignite the charge within. In artillery, priming powder, a fuse, squib, or friction igniter is inserted into the touch hole to ensure ignition of the charge.

The powder in the touch hole was lit either with a slow match, a linstock or a type of flintlock mechanism that was known as a gunlock.