The refresh command is similar to replot, with two major differences. refresh reformats and redraws the current plot using the data already read in. This means that you can use refresh for plots with in-line data (pseudo-device '-') and for plots from datafiles whose contents are volatile. You cannot use the refresh command to add new data to an existing plot.
Mousing operations, in particular zoom and unzoom, will use refresh rather than replot if appropriate. Example:
plot 'datafile' volatile with lines, '-' with labels
100 200 "Special point"
e
# Various mousing operations go here
set title "Zoomed in view"
set term post
set output 'zoom.ps'
refresh