Star rarity
From PSU Cyril Wiki
Star Rarity is basically how rare something is, measured in stars.
For example, a four star item is more rare than a two star item. it represents item tiers - More often than not, the higher the star count, the "better" the item is. Though this is not always the case, as such with Phantasy Star Online. For example, Slicer of Fanatic was the "best" slicer in the game, but it was only nine stars our of a possible twelve; nine being the threshold for rarity. Six stars will equal a rare, on certain terms (A Moon Atomizer is not rare). Also, the Meseta values of items seem to be dependent of their star rarity to some extent.