Blockchain

As you've previously seen, each block has a reference to the previous block (via the parent hash). By tracing back each block by their parent hash, we can reach the genesis block. This ordering of blocks is the blockchain.

This structure has two important properties depending on which blocks you consider:

If we trace only finalized blocks, we get a linear list of blocks where the index equals the height of the block.

If we include non-finalized blocks as well, we get a tree of blocks, since forking can happen before finalization.

Relay Chain

The Relay Chain refers to Polkadot, or its testnet equivalent, Paseo. Every Parachain is connected to the Relay Chain.

The Relay Chain provides two main features:

• Block finalization for Parachains.
• Cross-chain communication between Parachains via XCM (Cross-Consensus Messaging).

Parachain

A Parachain is a blockchain connected to the Relay Chain. Mosaic Chain is a Parachain on the Polkadot Relay Chain.

Each Parachain runs its own Runtime — the on-chain logic that defines how blocks are produced and transactions are processed. This is what allows Mosaic Chain to have its own rules and features, independent of other Parachains. For a broader overview of the Polkadot architecture, see the Polkadot documentation.