Screen or Tera Term is an open source 'tty multiplexor'. Or in English, it allows you to run multiple programs on UNIX and easily jump between them. Screen can be thought of as a 'text mode' "alt tab" like what exists in Windows to cycle thru running programs.
The big advantage of screen, is that you can detach the screen sessions, and logout while the programs continue to run. You can also re-attach your screen session, like you have never left. This can be vital if you have a connection that is prone to dropping, and you need to do something that cannot be interrupted.
Command line options
Use: screen [-opts] [cmd [args]] or: screen -r [host.tty] Options: -a Force all capabilities into each window's termcap. -A -[r|R] Adapt all windows to the new display width & height. -c file Read configuration file instead of '.screenrc'. -d (-r) Detach the elsewhere running screen (and reattach here). -D (-r) Detach and logout remote (and reattach here). -e xy Change command characters. -f Flow control on, -fn = off, -fa = auto. -h lines Set the size of the scrollback history buffer. -i Interrupt output sooner when flow control is on. -l Login mode on (update /etc/utmp), -ln = off. -list or -ls. Do nothing, just list our SockDir. -L Terminal's last character can be safely updated. -m ignore $STY variable, do create a new screen session. -O Choose optimal output rather than exact vt100 emulation. -q Quiet startup. Exits with non-zero return code if unsuccessful. -r Reattach to a detached screen process. -R Reattach if possible, otherwise start a new session. -s shell Shell to execute rather than $SHELL. -S sockname Name this session <pid>.sockname instead of <pid>.<tty>.<host>. -t title Set title. (window's name). -T term Use term as $TERM for windows, rather than "screen". -v Print "Screen version 3.07.01 (FAU) 20-Nov-95". -wipe Do nothing, just clean up SockDir. -x Attach to a not detached screen. (Multi display mode).