A toggle bolt is a fastener

Fastener

A fastener is a hardware device that mechanically joins or affixes two or more objects together.Fasteners can also be used to close a container such as a bag, a box, or an envelope; or they may involve keeping together the sides of an opening of flexible material, attaching a lid to a container,...

 for hanging things on hollow walls such as 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...

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Toggle bolts have wings that open inside a hollow wall, bracing against it to hold the fastener securely.

The wings are much larger than the bolt they are attached to. This spreads the weight of the secured item over a larger area, increasing the weight that can be secured compared to a regular bolt.