In Unicode, a Private Use Area (PUA) is a range of code points that, by definition, will not be assigned characters by the standard.
Private-use characters are assigned Unicode code points whose interpretation is not specified by this standard and whose use may be determined by private agreement among cooperating users.
Historically, planes E0 (224) through FF (255), and groups 60 (96) though 7F (127) of the Universal Coded Character Set (i.e. U+E00000 through U+FFFFFF and U+60000000 through U+7FFFFFFF) were also designated as private use.
Some of these private use agreements are published, so other PUA implementers can aim for unused or less-used code points to prevent overlaps.
One of the more well-known and broadly implemented PUA agreements is maintained by the ConScript Unicode Registry (CSUR).
Tolkien's cursive and runic scripts), Alexander Melville Bell's Visible Speech, and Dr. Seuss' alphabet from On Beyond Zebra.
This project is attempting to support all of the scribal abbreviations, ligatures, precomposed characters, symbols, and alternate letterforms found in medieval texts written in the Latin alphabet.
[needs update] Some agreed-upon PUA character collections exist in part or whole because the Unicode Consortium is in no hurry to encode them.
[8] The concept of reserving specific code points for Private Use is based on similar earlier usage in other character sets.