A parachain is a blockchain connected to Polkadot’s relay chain that maintains its own state and transaction rules while participating in shared security. It can specialize in an application or service rather than reproducing one universal execution environment. A parachain is a chain with its own runtime, not simply a smart contract deployed on another chain.
Collators and shared validation
Collators maintain parachain state and assemble proposed blocks with the data needed to check them. Relay-chain validators verify candidates against the parachain’s registered state-transition rules. Polkadot’s wider validation and finality processes determine which candidates become accepted history.
This division lets different parachains process work in parallel without each having to establish a completely separate security validator set. It does not make collators and relay-chain validators interchangeable roles.
Resources and communication
Access to validation resources is scheduled through coretime. Polkadot’s Agile Coretime supports bulk allocation and on-demand access; older descriptions centered only on long-term slot auctions do not capture the current model.
Parachains can exchange messages using the XCM format and supported transport mechanisms. Applications still need compatible permissions and asset handling.
Shared security does not certify application logic, governance decisions, or external bridges. A parachain’s practical behavior also depends on its runtime, collator availability, and allocated resources.