Wide-spread web fonts

The following fonts are supported by most browsers on most platforms and can thus be considered "web-safe". In order to give you an idea how the different fonts look like, I've applied them to their corresponding paragraph.

Verdana

Verdana is a sans-serif typeface designed in 1996 for Microsoft Corporation. It was designed to be readable at small sizes on a computer monitor. It is characterized a large x-height, wide proportions and loose letter-spacing.

Georgia

Georgia is a serif typeface designed in 1996 for Microsoft Corporation. It was designed to be readable at small sizes on a computer monitor.It is similar to Times New Roman but larger.

Helvetica

Helvetica is a sans-serif typeface designed in 1957 in Switzerland (thus the name). It was designed as a neutral typeface with great clarity. It is one of the most widely used sans-serif typefaces.

Trebuchet MS

Trebuchet MS is a sans-serif typeface designed in 1996 for Microsoft Corporation. It was designed especially for computer screens and is especially adapted for headlines.

Lucida Sans Unicode / Lucida Grande

Lucida Sans Unicode is a sans-serif typeface which was first shipped with the Microsoft Windows NT 3.1. It is one of the most ideal for upside-down text. Lucida Grande is a nearly identical font available on Mac OS X.

Tahoma

Tahoma is a sans-serif typeface designed in 1994 for Microsoft Corporation. It was designed especially for legibility on the screen. It is similar to Verdana, but has a narrower body, less generous counters and much tighter letter spacing.

Typography terminology

Typeface
A typeface is a set of characters sharing the same design. For example, Arial, Helvetica, Times and Verdana are typefaces.
There are two different categories of typefaces: serif and sans serif.

Font
A font is a specific size (usually defined in points) and style (roman, italic, bold, extrabold, condensed, etc.) of a typeface. For example, Verdana 12 pt bold is a font.

Serif
Serif typefaces use small decorative marks to embellish characters and make them easier to read. Times Roman is an example of a serif typeface.

Sans serif
Sans serif typefaces are composed of simple lines unlike Serif typefaces. Helvetica is an example of a sans serif typeface.

Times (serif type)	Helvetica (sans serif)
Roman	Roman
Bold	Bold
Italic	Italic

Baseline
The baseline is an imaginary line on which most of the characters "sit". The baseline is also relevant for measurements (including x-height and leading) and for alignment purposes.

Mean line
The mean line (or midline) is also an imaginary line running along the top of non-ascending, lowercase letters (e.g. "p" or "x") and at the curve of some ascending letters (e.g. "h").

Ascender
It is the part of a lower case letter (e.g. "t" or "b" which goes above the mean line.

Descender
It is the part of a lower case letter (e.g. "q" or "g" which goes below the baseline.

Point
Types are measured in points (pt). One point is equal to 1/72 of an inch (i.e. 0.3527 mm).

X height
It is the distance between the baseline and the mean line of the font. In most fonts it corresponds to the height of the lower case letter "x".

Font size
It is also called "point size" or "type size". It's the distance from the ascender line to the descender line. It corresponds to 1em.