A heraldic picture is called an emblazon. Emblazons are visual manifestations of heraldic insignia, typically displayed on shields or flags. Because emblazons are awkward to work with, heraldry uses a specialized jargon called blazon to describe shields and flags. Persons skilled in heraldry can discuss shields entirely in blazon, without ever drawing the emblazons. As a noun, the word "blazon" is also used to refer to the heraldic description of a shield or flag.
The great advantage of blazon over plain English is that blazon terms are defined more precisely than English ones. As a result, one can describe a shield more accurately and in fewer words with blazon than one can in plain English.
The distinction between blazon and emblazon is an important one, since there is not a one-to-one correspondence between blazons and emblazons. In many cases, a particular emblazon can be blazoned (=described in heraldic language) in more than one way. And no two heraldic artists will emblazon (=draw) a given blazon in exactly the same way. But for well-designed heraldry, the blazon captures the important features of the emblazon, and, given a blazon, a trained heraldic artist should be able to produce a reasonable facsimile of the original emblazon.