set <axis>label <text> [ rotate <angle> ]
The setting xlabel sets the label which should be written along the x-axis. For example,
set xlabel '$x$'
sets the label on the x-axis to read ‘’. Labels can be placed on higher numbered axes by inserting their number after the ‘x’; for example,
set x10label 'foo'
would label the tenth horizontal axis. Similarly, labels can be placed on vertical axes as follows:
set ylabel '$y$' set y2label 'foo'
An optional rotation angle may be specified to rotate axis labels clockwise by arbitrary angles. The angle should be specified either as a dimensionless number of degrees, or as a quantity with physical dimensions of angle.