5.23.55 xlabel

set xlabel '<text>'

The xlabel setting controls the label placed on its $x$-axis (abscissa). For example:

set xlabel '$x$'

sets the label on the $x$-axis to ‘$x$’. Labels can be placed on higher axes by inserting their number after the ‘x’, for example:

set x10label 'foo'

would label the tenth $x$ axis.

Similarly, labels can be placed on $y$-axes as follows:

set ylabel '$y$' 
set y2label 'foo'