“picons” is short for “personal icons”. They”re small, constrained images used to represent users and domains on the net, organized into databases so that the appropriate image for a given e-mail address can be found. Besides users and domains, there are picons databases for Usenet newsgroups and weather forecasts. The picons are in either monochrome XBM format or color XPM and GIF formats.
These databases have been compiled in hopes of helping make cyberspace a more personable place. With them, software and services can be developed to identify persons on the net by face (or, at least, by institution logo) instead of by a cryptic e-mail address. Software of this kind is for example xfaces and exmh.