Hot melt adhesive also known as hot glue, is a form of thermoplastic

Thermoplastic

Thermoplastic, also known as a thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently...

 adhesive

Adhesive

An adhesive, or glue, is a mixture in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. The types of materials that can be bonded are vast but they are especially useful for bonding thin materials...

 that is commonly supplied in solid cylindrical sticks of various diameters, designed to be melted in an electric hot glue gun. The gun uses a continuous-duty heating element

Heating element

A heating element converts electricity into heat through the process of Joule heating. Electric current through the element encounters resistance, resulting in heating of the element....

 to melt the plastic glue, which may be pushed through the gun by a mechanical trigger mechanism, or directly by the user. The glue squeezed out of the heated nozzle is initially hot enough to burn and blister skin.