Perhaps the phrase was designed to mitigate caveats of either one or another... What would these have been?
And secondly, realistically, would a court ever uphold the difference between a settlement described in one of these terms but not both?
A “full and final settlement” is a complete resolution of all matters in dispute between the parties.
This can be contrasted with both a partial settlement, which resolves some but not all issues, and an interim settlement, which means something still remains to be done.
A partial settlement probably needs no further explanation - some things are dealt with and some things aren’t.
An interim settlement an be almost anything: