Just like EOS or Telos, Ethereum is a blockchain — a decentralized digital ledger. Ethereum is considered to be a trailblazer of programmable blockchains, aiming to solve the inherent problems of BTC — the first cryptocurrency.
Ethereum is based on a different type of underlying protocol, which makes some things drastically different from EOSIO. EOS & Telos themselves, in turn, were created to improve on things that made Ethereum less user-friendly — high costs, high entry barrier, high amounts of power consumption, vulnerability to sybil attacks and so on.