The default terminal that is active at the time of program entry depends on the
system platform, gnuplot build options, and the environmental variable GNUTERM.
Whatever this default may be, gnuplot saves it to internal variable GNUTERM.
The unset terminal command restores the initial terminal type.
It is equivalent to set terminal GNUTERM. However if the string in GNUTERM
contains terminal options in addition to the bare terminal name, you may want
to instead use set terminal @GNUTERM.
