Relay Chain: Polkadot’s “heart,” helping to create consensus, interoperability and shared security across the network of different chains; Parachains: independent chains that can have their own tokens and be optimized for specific use cases; Parathread: similar to parachains but with flexible connectivity based on an economical pay-as-you-go model; Bridges: allows parachains and parathreads to connect and communicate with external blockchains like Ethereum.