Fonts are structured in three main categories, based on the type of lettering stroke.
Serif fonts are identified by the use of small extensions (serifs) at the end of the stroke, and are commonly used in book and newspaper text.
San-serif, or letters without serifs, commonly known as "block letters", are normally used for headlines and displays- where simple letter construction for increased readability is desired.
Script fonts are used to simulate cursive handwriting, and are used for printed pieces which are formal in nature.
Symbols are often thought of as a separate type of font. While there are unique symbol fonts, such as those used for musical, mathematical, scientific, architectural, or general utility use, many symbols are actually designed to be related to a particular font classification.
The major font categories are separated into classifications. Each may have thousands of variations, but each classification will feature the same basic elements of construction: serif, san-serif or script. Font classifications include: Ornamental or decorative, ethnic, display, text and calligraphic.
Typefaces are individual fonts, of which there are many thousands. Typefaces can be sub-grouped into font "families," consisting of fonts with similar design features. Common type families include: Times Roman, Helvetica, Blackletter, Gothic and others. Each family includes variations of the font, in what is called "font style".
Font styles are variations of a particular typeface, which include bold and italic. Font styles are used to accentuate words or phrases, and are designed to compliment the original style without deviating from the basic design elements.
Font lettering is measured in "points", which reflect the measurement of the tallest letter in the font, and "picas", which are used to measure the length of a word, paragraph, or sentence. The space between letters is called "kerning", and the space above and below lines of type is called "leading".
Printers and typesetters use select font categories, families and typefaces for most general work. While the use of particular typefaces is hugely varied, and based on personal preference and client approval, serif fonts in the Times Roman, Garamond, and Goudy families are frequently used for text, while sans-serif fonts in the Helvetica and Gothic families are widely used for headlines. Script, ornamental, and other decorative fonts are normally reserved for specialty printing of advertisements, announcements and marketing material headlines.