A font and a typeface are not the same thing, and the difference is metal
People use font and typeface interchangeably, but typographers do not. A typeface is a design, such as Times. A font was originally a physical box of metal letters in one size and style, so 8-point Caslon Italic and 10-point Caslon Italic counted as two separate fonts.
A typeface is the set of shapes for letters, numbers and symbols, each individual shape being a glyph. Variations in weight, slope and width build a family: Times Roman, Times Italic and Times Bold are separate typefaces within the Times family. Historically a font was what a foundry actually shipped, a set of cast pieces called sorts with multiple copies of each character. Today the font is the software file that delivers a typeface to the screen, and because digital outlines scale freely, a single file covers every size.
The idea of large, deliberately planned families is surprisingly recent. The first extended families, with many widths and weights in one style, appeared in the early 1900s, beginning with a face called Cheltenham. Around 1910 the designer Morris Fuller Benton drew a sans-serif companion to an existing serif face, arguably creating the first superfamily, which groups structurally different designs that share a clear visual relationship.
Measurement has its own quirks. Type is sized in points, now usually one seventy-second of an inch, but the size refers to an invisible box called the em square rather than any visible letter. Set Helvetica at 12 points and no single part of it need measure exactly 12 points. Simply enlarging a shape can also look wrong, so designers speak of optical size, the viewing size a design was intended for.
Movable type was invented in China, but its thousands of characters discouraged complete typefaces. Johannes Gutenberg's key breakthrough in the 15th century was an adjustable mould that could cast letters of any width, from a broad M to a slim l, and a lead alloy that cooled quickly.
Source: Typeface
