What are people's definitions of an "L3"?

Particularly, is it an architectural classification (whether or not there's some kind of intermediary between it and L1), or a security classification (can the attacker steal? can they freeze funds? can they steal/freeze but only at high cost?)

L3 I’ve thought would be proprietary. In a gaming context, a game would have its items on an L2 but if the game itself was on chain (like opminecraft) that would happen on a private chain optimized for the games requirements and would interact with the “public” L2 as needed.

At least that’s the model I imagine