The concept of offline reading comes from BBS world where a user
connects via a modem to the bbs, and downloads a file (usually
called a packet) containing all unread messages since the last
connection. Then a program is used, to extract the messages from the
packet, read them and reply to them, creating a reply packet to be
uploaded at the next connection.  This saves time (the bbs lines are
less engaged) and money (on phone bills).  It also means that the
user can make use of much friendlier reading tools than can be made
available in an interactive login environment.

For the purposes of this FAQ, "offline" is defined to mean the
following:  "transferring mail and news in some form from an existing
interactive account to a user's machine, usually via a modem, so
that the messages may be read while the user is not connected to the
account, and so that replies may be composed to be uploaded to the
account at some later time to be injected into the network".