The W3C has published a first public working draft of the WOFF font format specification.
The WOFF font format is designed to provide lightweight, easy-to-implement compression of font data, suitable for use in conjunction with the @font-face CSS declaration.
"This document specifies a simple compressed file format for fonts, designed primarily for use on the web. The WOFF format is a container for the table-based sfnt structure used in TrueType, OpenType and Open Font Format fonts, which are collectively referred to as sfnt-based fonts. A WOFF file is simply a repackaged version of a sfnt-based font with optional compression of the font data tables. The WOFF file format also allows font metadata and private-use data to be included separately from the font data. WOFF encoding tools convert an existing sfnt-based font into a WOFF formatted file, and user agents restore the original sfnt-based font data for use with a web page."
You can read the entire document here.