These are for BashSh and possibly ZshShell
EDITOR # which editor to use by default
VISUAL # like EDITOR, sometimes VISUAL takes precedence
PWD # present working directory
USER # username
UID # uid number
SHELL # shell name
DISPLAY # X11 display to use
PATH # : separated list of directories to search for commands
CDPATH # : separated list of directories to search when using cdCDPATH
The CDPATH variable allows cd to search a list of directories for directories to cd into, rather than just the current directory.
CDPATH=/usr
cd bin # will end up in /usr/bin
CDPATH=$HOME:/usr
cd bin # will end up in $HOME/bin if present, else /usr/bin