Old name with a very specific meaning. The therm "Little Rus" was first used for Kyiv in sense of it being the center of Rus - Rus proper and "Greater Rus" meant the wider area of their influence. Russians (as we know them today) managed to turn this around and made it a derogatory term.
And "Little Russia" is an old name of a geographical region (which somewhat corresponds to the traditionally Russian-speaking parts of Ukraine).