In heraldry and heraldic vexillology, a blazon is a formal description of a coat of arms, flag or similar emblem, from which the reader can reconstruct the appropriate image. The verb to blazon means to create such a description. The visual depiction of a coat of arms or flag has traditionally had considerable latitude in design, but a verbal blazon specifies the essentially distinctive elements. A coat of arms or flag is therefore primarily defined not by a picture but rather by the wording of its blazon (though in modern usage flags are often additionally and more precisely defined using geometrical specifications). Blazon is also the specialized language in which a blazon is written, and, as a verb, the act of writing such a description. Blazonry is the art, craft or practice of creating a blazon. The language employed in blazonry has its own vocabulary, grammar and syntax, which becomes essential for comprehension when blazoning a complex coat of arms.

Other armorial objects and devices – such as badges, banners, and seals – may also be described in blazon.

The noun and verb blazon (referring to a verbal description) are not to be confused with the noun emblazonment, or the verb to emblazon, both of which relate to the graphic representation of a coat of arms or heraldic device.