An “Endpin” is a small ‘knob-like’ component on a guitar that attaches the guitar strap to the guitar, located at the tail end of the guitar. It is used to hold the guitar strap so you can play stood up. With many electric acoustic guitars, the Endpin also has the output jack installed for routing the signal out of the instrument’s picks up and into an amplifier. These are formally known as Endpin Jacks.