Polygon is a cryptocurrency, with the symbol MATIC, and also a technology platform that enables blockchain networks to connect and scale. Polygon—"Ethereum's internet of blockchains"— launched under the name Matic Network in 2017.1

The Polygon platform operates using the Ethereum blockchain and connects Ethereum-based projects. Using the Polygon platform can increase the flexibility, scalability, and sovereignty of a blockchain project while still affording the security, interoperability, and structural benefits of the Ethereum blockchain.
MATIC is an ERC-20 token, meaning that it's compatible with other Ethereum-based digital currencies. MATIC is used to govern and secure the Polygon network and to pay network transaction fees. (Source: https://www.investopedia.com/polygon-matic-definition-5217569)