A font is a mapping from characters to glyphs. Your handwriting style could well be considered to be a (very, very complex) font, though the term is more generally used for cases where the mapping is more clearly defined, such as in printing or displaying text on a computer screen.
There are vast numbers of fonts available for computers, but it is probably a good idea not to use very many at once.
Need more here, especially references to background works elsewhere on the Web...
See also:
Category Concept | Characters, glyphs, code-points, and byte-sequences