1. The process of making glass, metal, or alloy less brittle by exposing it to heat and then to being cooled.
2. To subject glass or metal to a process of heating and then slow cooling in order to toughen and to reduce brittleness.

A heat treatment applied to metals.

Annealing is more often applied to the reduction of the hardness of a metal; however, annealing can also be done to change the microstructure of a metal or to achieve a specific set of physical or mechanical properties.

In the annealing process, the metal is first heated to a predetermined temperature and then it is allowed to cool to room temperature. It is often an important step in the production of specific metal types.

In the production of fine wires, there may be several intermediate annealing steps before the metal is drawn through fine openings to produce wirea with the desired properties.