What's the deal with orange items without stats?
Is there some kind of wow-equivalent item quality level for orange items in swtor?
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It does not mean "Legendary" like in WOW.
It means that the item consists of Mod slots, and it's primarily the mods that make up the actual bonuses of the item. The base item will still have some minor bonuses (like the difference in armor between light armor, medium armor, and heavy armor). However, all unmodded orange items of the same category will be equal in power. You would choose one orange item over another based on the looks.
Since mods can be removed and replaced at will, it is often worthwhile to keep even the very first orange items you find in the bank even after the mods on them are getting out of date, since as soon as you buy or find some updated mods, you can bring them back up to relevance.