Sharding is a very simple to understand concept and it's used in database systems today. Effectively, Ethereum's long-term data will become split across 4 parti

Sharding is a very simple to understand concept and it's used in database systems today. Effectively, Ethereum's long-term data will become split across 4 partitions (which function as one chain). A validator would not be required to validate data on all 4 shards, they could validate across just one. Ethereum's execution will continue to be serialized while the data layer is parallelized. This allows the chain data to grow without excessive hardware requirements.