The 'screen' application provides this functionality. You can start a teminal session via screen, drop the connection and reconnect to the session again, at a later point in time. This is usfull when doing remote administration over an un reliable connection.
Installing screen on FreeBSD isn't hard:
First make sure you'v installed and updated the entire ports tree.
# cd /usr/ports/misc/screen
# make install
Using screen isn't hard too:
Starting a session:
screen -S <name of this session>
Detach from within a session, but keep the session running:
Reattach to a session:
screen -r <name of the session>(if there's only one session running, the name is optional)