A pintle is a pin or bolt, usually inserted into a gudgeon, which is used as part of a pivot or hinge.
A pintle/gudgeon set is used in many spheres, for example: in sailing to hold the rudder onto the boat; in transportation a pincer-type device clamps through a lunette ring on the tongue of a trailer; in controllable solid rocket motors a plug moves into and out of the motor throat to control thrust.
In the military, a pintle is used with light machine guns as the mounting hardware that mates the machine gun to a tripod. Essentially the pintle is a bracket with a cylindrical bottom and a cradle for the gun on top; the cylindrical bottom fits into a hole in the tripod while the cradle holds the gun.
In rocketry, a pintle engine uses a single-feed fuel injector rather than the hundreds of smaller holes used in a typical rocket engine. That lowers the cost of engine manufacture while surrendering some performance. Originally developed by Grumman for the Apollo Lunar Module, notable modern uses are on the engines developed by SpaceX.
Pintle is also an archaic word for the penis, current in Scottish vernacular use.