http://www.fmi.uni-passau.de/archive/doc/unix/unixhelp/Unixhelp/glossary_gm.html (Einblicke ins Internet, 10/1995)information contained in every mail message which is used by mail programs to provide the user with a summary of the origin and contents of each message.
a single character that is used in place of another character or set of characters.
the execution of two or more processes at the same time.