Polkadot is a blockchain platform designed to let multiple independent blockchains, called parachains, connect to a central chain and communicate with one another. This addresses a common limitation in the blockchain space, where most networks operate in isolation and cannot easily exchange data or assets with other chains.
Each parachain can be customized for a specific purpose, such as a particular DeFi application or gaming platform, while still benefiting from the shared security provided by Polkadot's central Relay Chain. This shared security model means individual parachains do not need to build their own validator network entirely from scratch.
The native token, DOT, is used for network governance, allowing holders to vote on proposed changes, as well as for securing a parachain slot through a process called staking or, historically, through auctions.