What does go bygone mean?

Excuse me, could you please clarify the meaning of the phrase "go bygone"? I've come across it in a few contexts recently and I'm struggling to grasp its exact significance. Is it referring to something that has passed, perhaps in the sense of being outdated or no longer relevant? Or does it have a more nuanced meaning that I'm missing? I'd appreciate any insight you can provide to help me better understand this phrase.