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?)

modularity of cosmos but with the security of ethereum 

that sentence was mainly to attract readers

l3s give the possibility to use different da solutions that will help to get new use cases that require less security guarantees (e.g games / social)  - we cant get with dapps that need to publish data on ethereum