The Layer-1 blockchain refers to a set of solutions that strives to improve the base protocol to add scalability. Sharding and consensus protocol changes are two of the most commonly used Layer-1 solutions.
The consensus protocol change made drastic improvements to the Ethereum blockchain. It shifted towards using the less energy-wasteful protocol including proof-of-stake (PoS) instead of proof-of-work (PoW).
Similarly, sharding also adds scalability to the entire blockchain network. Instead of adding sequential transactions to a network, every single transaction is broken down into small data sets known as ‘shards.’ Each unit is processed in parallel in the network.