A style, is autocad-speak for a name one assigns to a formatted font.
When one defines a STYLE one is essentially naming a standard format for text,
as in use font simplex, use a 0.80 width factor, be annotative, or not, use an obliqued angle.
One would do well to think of text styles really, as text formats.
Fonts on the otherhand are or can be copyrighted FORMS of the various letters and symbols
contained in that particular typeface. A common type face is the venerable Times Roman,
this particular font can come in many different formats (styles in autocad) BOLD, italicized, however
the text is display it's font name remains Times New Roman.
STYLE=Format
FONT=the shape of the letters and symbols