A font substitution system (in full, PANOSE 1.0) stored in TrueType fonts as 10 digits in the *'OS/2' table. Applications wishing to determine the closest installed font to a requested, but absent, font compute the typographic "distance" (that's a distance measured in 10-dimensional PANOSE-space!) from each installed font to the requested one, whose PANOSE bytes are known. Finally, the installed font with the minimum distance is used. The system was developed by ElseWare Corporation, which was taken over by Hewlett-Packard. There's also PANOSE 2.0, a major extension into parametric font territory. The PANOSE 2.0 White Paper describes the system in some detail.
A font-classification method that measures values, such as serifs, weight, and stroke variations, for a TrueType font. These values are represented by a Panose number. The Panose number is then used to associate the font with other fonts of similar appearance but different names. The closer the Panose number of two fonts, the more similar they are.
The PANOSE System is method for classifying typefaces solely on their visual characteristics. It can be used to identify an unknown font from a sample image or to match a known font to its closest visual neighbor from a pool of candidates.