A type of Layer 2 solution built on top of bitcoin and other existing blockchains to boost system processing.
The Lightning Network is the most popular example of a Layer 2 solution built on bitcoin (and litecoin) for better system processing and scalability. Built over an existing blockchain system, the Lightning Network serves as a complementary framework which allows user transactions to be executed significantly faster than on the original blockchain system. This is because it relies on user-generated channels to increase transactions across involved nodes.
Even though the Lightning Network as a Layer 2 solution is somewhat semi-independent, it still borrows the stability of the underlying system to be effective and relevant.