What are fonts?

When printing was done with metal type, a font was the the source, or matrix, from which type was cast, or a set of type in one size and style cast from the same font. Now, in the strictest definition, a font is a single weight of a single width of a single style of a single typeface, either unsized or in a single size. Unless the term font is qualified, this is its meaning in this publication.

Weight
Weight is the lightness or darkness of the printed characters. Heavy characters have thicker lines and look blacker than light characters. Typical weights are:
Medium
Bold

Width
Width, or proportion, is determined in relation to a character's height. Typical widths are:
Condensed
Normal
Expanded

Style
Style, or posture, is the inclination of a letter around a vertical axis. Typical styles are:
Roman
Italic

Typeface
A typeface is the design from which fonts are created. It is usually either copyrighted or registered as a trademark of an owner.
Typical typefaces are: 
Courier
Helvetica
Times New Roman