Lore
Etymology
From Old English lār, "learning, instruction." The modern slang narrows a fandom and video-game sense — a game’s "lore" is its deep background story — and applies it, half-jokingly, to actual people and their tangled histories, a use that spread widely online around the early 2020s.
noun · /LOR/
The accumulated backstory and context around a person or thing — the history you’d need to know to fully get them.
What it names
It treats a real person’s life like a fictional universe’s canon: the running saga of their exes, feuds, in-jokes, and past disasters. To say someone has "a lot of lore" is to say they come with chapters you have to catch up on.
Example
Before you meet my family, you need some lore, because Thanksgiving is going to be tense.
Related idea
Broader than a backstory, which is usually one origin tale; lore is the whole sprawling, ongoing archive.