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?)

Right now when I hear L3 I feel annoyed. My understanding is that L2s are still not 100% without training wheels, e.g. sequencers, 7 day withdraw period, etc. Also unclear how composability and liquidity works among competing L2s, so L3 isn‘t something I‘m interested in. L2s need to improve.