A list of people who all receive the same
news or information. Before the
advent of near-universal e-mail, a distribution list
was simply a list of initials at the bottom of a
cover sheet. Admins (who at that
were called "secretaries") would
have to go down to the Xerox room and
make photocopies for everyone.
Now, a distribution list is the cc: field in
the e-mail header, or, at slightly
sophisticated companies, a simple e-mail alias.