Tether provides a secure, fast, and low-cost way to store, send, and receive money on the Blockchain.
Tether (USDT) is basically a cryptocurrency of its own and one tether or one token represents one US dollar in value and that's pegged to the reserves the tether company has in their bank accounts. Tether is called a stablecoin because it is claimed to always be worth $1.00, though sometimes fluctuates a bit.
Tether is an ERC20 token on the Ethereum blockchain. ERC20 is a protocol standard for issuing tokens on Ethereum’s network.