In typography, a font is traditionally defined as a complete character set of a single size of a particular typeface. For example, all characters for 9 point Bulmer is a font, and the 10 point size would be another font. For the origin and evolution of fonts, see History of western typography. ...
Since the introduction of personal computers, and an accompanying larger group, not professionally trained in typography, using type, a broader definition has evolved. The term font is now often used as a metonym for a typeface. In rhetoric and cognitive linguistics, metonymy (in Greek meta = after/later and onoma = name) is the use of a single characteristic to identify a more complex entity. ...
References
Blackwell, Lewis. 20th Century Type. Yale University Press: 2004. ISBN 0-300-10073-6.
Fiedl, Frederich, Nicholas Ott and Bernard Stein. Typography: An Encyclopedic Survey of Type Design and Techniques Through History. Black Dog & Leventhal: 1998. ISBN 1-57912-023-7.
Lupton, Ellen. Thinking with Type: A Critical Guide for Designers, Writers, Editors, & Students, Princeton Architectural Press: 2004. ISBN 1-5689-8448-0.
Macmillan, Neil. An A–Z of Type Designers. Yale University Press: 2006. ISBN 0-300-11151-7.