Golpe is mostly used in Flamenco guitar. A flamenco guitar is a type of Classical guitar, built for the purpose of playing Flamenco music It is a finger tap on the golpeador ("pick guard"). A pickguard (also known as scratchplate or golpeador in Flamenco music, and uncommonly a fingerrest) is a piece of plastic or other laminated
Technique
It is usually performed with the middle or annular (ring) finger, and can be performed either simultaneously with a downstroke performed by another finger (eg. simultaneous downstroke with index finger and golpe with annular finger), or independently in order to accent off beats.
As it requires the strumming finger and the golpe finger to move in opposite directions at the same time, it can be a little tricky to get used to.