The Probert Encyclopaedia of Heraldry

GYRON

In heraldry, a gyron is a subordinary of triangular form having one of its angles at the fesse point and the opposite side at the edge of the escutcheon. When there is only one gyron on the shield it is bounded by two lines drawn from the fesse point, one horizontally to the dexter side, and one to the dexter chief corner.
Research Gyron