Sweet norns are:
Originally this meant specific descendants of Sweet the first Sweet norn, created by Keltoi, with specific gene edits that cause high sex drive and immortality. They do not owe ancestry to the Essex Norns or other immortal variants such as Highlander and Zeus.
They are available on Muppetboy's Geatville
This term is now used more generally to refer to norns with a higher than usual life force that are very fertile, even if not related.