The terms font and typeface may seem similar but there is a difference.
Typeface: is the design of the alphabet–the shape of the letters that make up the type style. The letters, numbers, and symbols that make up a design of type. So when you say “Arial” or “Goudy” you’re talking about a set of letters in a specific style.
Font: is one weight, width, and style of a typeface.
Legibility: is a measure of how easy it is to distinguish one letter from another in a given typeface. How legible a typeface is designed to be depends on its purpose. Legible typefaces usually have larger closed or open inner spaces (counters).
Readability: is how easy words, phrases, and blocks of text can be read. Readability describes how a typeface is used on the page. Good typography makes the reader want to continue reading as the font is more readable.
Examples of Type Classifications thanks to Fonts.com
This category includes the first Roman types, originally created between the late 15th and mid 18th centuries, as well as typefaces patterned after those designed in this earlier period. The axis of curved strokes is normally inclined to the left in these designs, so that weight stress is at approximately 8:00 and 2:00 o’clock. The contrast in character stroke weight is not dramatic, and hairlines tend to be on the heavy side. Serifs are almost always bracketed in old style designs and head serifs are often angled. Some versions, like the earlier Venetian old style designs, are distinguished by the diagonal cross stroke of the lowercase.
English printer and typographer John Baskerville established this style in the mid 18th century. These typefaces represent the transition between old style and neoclassical designs, and incorporate some characteristics of each. Baskerville’s work with calendered paper and improved printing methods (both developed by him) allowed much finer character strokes to be reproduced and subtler character shapes to be maintained. While the axis of curve strokes can be inclined in transitional designs, the strokes normally have a vertical stress. Weight contrast is more pronounced than in old style designs. Serifs are still bracketed and head serifs are oblique.
Typefaces in this category tend to emulate lapidary inscriptions rather than pen-drawn text. Contrast in stroke weight is usually at a minimum, and the axis of curved strokes tends to be vertical. The distinguishing feature of these typefaces is the triangular-shaped serif design, or a flaring of the character strokes where they terminate. In some type classification systems this category is sub-divided into two groups: “glyphic” and “latin.” “Latins” are faces with strictly triangular-shaped serifs.