The set xlabel command sets the x-axis label that is centered along the x axis. Using the optional x,y screen offsets, the label can be placed anywhere on the plot. set xlabel with no parameters clears the label.
Syntax:
set xlabel {"<label>"} {<xoff>}{,<yoff>}
show xlabel
Specifying constants <xoff> or <yoff> as optional offsets for the label will move the label <xoff> or <yoff> character screen coordinates. For example,
set xlabel -1
will change only the x offset of the xlabel, moving the label roughly one character width to the left.
(The EEPIC, Imagen, LaTeX, and TPIC drivers allow 
in a string to specify
a newline.)