Cardano is a Proof of stake (PoS) blockchain platform and has a cryptocurrency called Ada. Compared to Proof of work (PoW) blockchains / cryptocurrencies like Bitcoin and Ethereum, which require a lot of electrical energy, Proof of Stake blockchains like Cardano do only require a minimal amount of electrical energy for running the servers which represent the network.
Holders of the Cardano cryptocurrency Ada can stake their funds to a staking pool like RENEW pool to get a yearly return on their investment of about 5%.
Read more on Wikipedia about Cardano, Proof of stake, Proof of Work and Decentralized finance