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.

If we do this tracing for only the finalized blocks, then we will get a list of blocks, where the index in this list equals to the height of the block.

If we check all blocks (including non-finalized blocks), we will get a tree of blocks, since forking can happen here.

Relay Chain

The Relay Chain refers to the Polkadot (or Paseo Tesnet). Every Parachain is connected to the Relay Chain.

The Relay Chain provides two main features:

• Provides finalization for the blocks on Parachains.
• Provides a centralized interface (XCM) for communication between different parachains.

Parachain

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