The legend refers to the block of information printed on the graph (or occasionally outside it) that explains which curve or symbol is associated with which quantity. It is called a key in gnuplot. A legend or some device that conveys the equivalent information is essential when the graph displays more than one curve.
You've probably noticed that all of our example graphs already contain a key; this is done by gnuplot by default. This recipe will show you how to take complete control of your graph's legend.
Following is a gnuplot script showing the extra commands that produce the legend in the previous plot:
set term ...