What does _( do to a string?

["Russell, Patrick" <patrick russell lmco com>]

Hello All,
        I was digging through some of the gnumeric impot/export routines and
noticed that some of the string values appear with _( ) around them, Why?
An example of this is at the bottom of the file
/opt/freeware/src/packages/BUILD/gnumeric(whatever build)/src/stf.c.  It
reads:
desc = _("CSV File import");

Thanks,
Pat