Any type of mold used for casting metal type.
In flexographic platemaking, a matrix is a mold made from an engraving or a metal relief master into which softened rubber is pressed. See Plate: Flexography: Rubber Plates.
In graphics, the term matrix is used to refer to any coordinate system or grid. See Grid.
In typesetting, a matrix is a metal mold or photographic image of a type character used to generate copies of that character during the setting of type.