A molly or molly bolt, commonly misspelled moly, is a formerly trademarked name for a specialized fastener used with drywall

Drywall

Drywall, also known as plasterboard, wallboard or gypsum board is a panel made of gypsum plaster pressed between two thick sheets of paper...

. Larger sizes permit reasonably heavy objects, such as shelving, flatscreen TV mounts or central heating radiators to be attached to drywall in locations where there is no stud

Wall stud

A wall stud is a vertical member in the light frame construction techniques called balloon framing and platform framing of a building's wall.-Purpose:...

 behind the drywall. For heavy objects, multiple molly bolts may be required.

Attaching

The fastener is an anchor, an expandable sleeve that slides into a hole drilled into the wall. A lip wider than the hole prevents it from falling behind the wall. A machine screw is then screwed into the sleeve, causing the anchor to bend, expand, spread and grip against the inside of the drywall.

Mollies come in various diameters and "grip lengths" for different drywall thicknesses and to support different loads.