Thermite is a pyrotechnic composition

Pyrotechnic composition

A pyrotechnic composition is a substance or mixture of substances designed to produce an effect by heat, light, sound, gas or smoke or a combination of these, as a result of non-detonative self-sustaining exothermic chemical reactions...

 of a metal powder

Powder metallurgy

Powder metallurgy is the process of blending fine powdered materials, pressing them into a desired shape , and then heating the compressed material in a controlled atmosphere to bond the material . The powder metallurgy process generally consists of four basic steps: powder manufacture, powder...

 and a metal oxide that produces an exothermic oxidation-reduction reaction known as a thermite reaction. If aluminium is the reducing agent it is called an aluminothermic reaction

Aluminothermic reaction

Aluminothermic reactions are exothermic chemical reactions using aluminium as the reducing agent at high temperature. The most prominent example is the thermite reaction between aluminium and iron oxides:-History:...

. Most varieties are not explosive, but can create short bursts of extremely high temperatures focused on a very small area for a short period of time. The thermite is simply a mixture of metal, often called the "fuel" and an oxidizer.