Ethereum 2.0(Eth2), refers to a set of interconnected upgrades that will make Ethereum more scalable, more secure, and more sustainable.
With this upgrade, Ethereum will move from PoW to PoS, and introduce sharding. The Ethereum network will significantly reduce energy requirements, allow more transactions to be processed simultaneously, and improve network security.
Eth2 will be phased in, and the Beacon Chain, the first major upgrade to Eth2, went live on December 1, 2020. You can read the official Ethereum 2.0 introduction to learn more about Eth2.