Newer Player here, what are these Legacies??

As the title asks. I only got into the game about 2ish months ago, but have seen other players mentioning these legacies weapons, especially after this past update. Are these just a configuration of mods that no longer drop? If so what is the combo? We're these rewards long since removed?

Just really trying to understand. Thanks.

submitted by /u/Griever2112
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