There’s never any exact lines. As with every term, especially in gaming, people will mean different things by it and may or may not implicitly assume people agree - except when arguing about it for ever and ever and ever. While nobody changes their mind at any point.

On something like Steam it’s a tag, which gives you limited information about the game. Not necessarily based on the literal reading, but what other stuff has/doesn’t have the same tag. And that’ll be inconsistent across storefronts, reviewers, individual players and all that stuff too.