The terms 'Ethereum, Solana, Polkadot and Tether', sometimes mentioned in the news, refer to

The terms Ethereum, Solana, Polkadot, and Tether refer to cryptocurrencies and blockchain-based digital assets. Ethereum is a prominent decentralized ledger-based blockchain platform that supports its native cryptocurrency, Ether [2]. Solana is a high-performance public blockchain platform designed for decentralized applications, with its native cryptocurrency being SOL [4]. Polkadot is a multi-chain interoperability protocol that allows different blockchains to transfer messages and value in a trust-free fashion. Tether (USDT) is a specific type of cryptocurrency known as a stablecoin, which is pegged to a reserve asset like the US Dollar to maintain a stable value. These digital assets utilize blockchain technology to enable peer-to-peer transactions without the need for a centralized government authority [3]. Unlike fiat currencies, they are not legal tender but are used for fundraising through Initial Coin Offerings (ICOs) and as digital stores of value [3].

Sources

1. [1] Indian Economy, Nitin Singhania .(ed 2nd 2021-22) > Chapter 7: Money and Banking > CRYPTOCURRENCIES > p. 160
2. [2] Indian Economy, Nitin Singhania .(ed 2nd 2021-22) > Chapter 9: Agriculture > IMPORTANT TERMS RELATED TO STOCK MARKET > p. 279
3. [4] https://en.wikipedia.org/wiki/Solana_(blockchain_platform)
4. [3] Indian Economy, Vivek Singh (7th ed. 2023-24) > Chapter 2: Money and Banking- Part I > What are Crypto currencies? > p. 77