Sorry, I'm not familiar with any blockchain layer model. Do you have a reference to the model this "layer-2" comes from? Clearly we're not talking about the OSI network model.
Layer 2 protocols are just those that operate "on top of" a base protocol, such as Lightning Network (on top of Bitcoin), roll_up (on top of Ethereum), or POA Network (also Ethereum).
(I would argue that the terms are imprecise though -- some protocols are described as operating "on top of Ethereum", but have their own consensus etc. which can function without Eth, so they could also be viewed as layer 1s with a bridge.)
(I would argue that the terms are imprecise though -- some protocols are described as operating "on top of Ethereum", but have their own consensus etc. which can function without Eth, so they could also be viewed as layer 1s with a bridge.)