Button
To keep your strap on, to keep your neck on. . .
Tuners have buttons. They're the parts you grab:
Some are decorative, too:
This is a "strap button" for attaching the strap to the neck of an instrument:
Here's a violin button:
It's the part of the back that extends out and covers the end of the neck heel. The button is critical to the structural integrity a violin's neck joint.
Some fretted instruments have this kind of button, too:
This mandolin neck joint is substantially strengthened by the portion of the back glued to the base of the neck heel.