In typography and typesetting, a collection of special characters, such as mathematics, fractions, monetary symbols, or decorative symbols, such as ∑, √, ?, 1/2, 1/4, 1/8, $, ￥, ￡, *, ?, %, etc. Accents are also available as pi characters. (The characters themselves—whether they are available in a standard typeface or not—are called pi characters; when available only in special fonts—such as Zapf Dingbats—they are referred to as pi fonts.)
A type manufacturer can create customized pi fonts for special needs, and new software programs allow for the easy creation of special digital fonts. Special fonts were developed for television listings, for example. Other types of pi characters include , ‰, o, ￠, §, ?, π, #, @, etc.
In handset metal type, pi also referred to the type of one style mistakenly put in the storage drawer of another style. When setting handset type, one of these mismatched letters would be thrown into a box of "pi type," also known as the hell box, to be sorted out later or returned to the type foundry for a credit. Pi also referred to handset type that had spilled or collapsed, a feared occurrence blamed on the printer's devil—the apprentice.
It is unknown if the etymology of "pi character" has anything to do with the Greek letter (and mathematical symbol) pi (π). It may even come from the common word "pie" (indicative of something "jumbled together"), and pi type is also known as pied type.