On-chain data availability

On-chain data availability occurs when an L2 publishes its transaction data to its designated L1. For example, a Celestia L2 that publishes its transaction data to Celestia is using on-chain data availability. If that Celestia L2 publishes its transaction data somewhere other than Celestia, it is using off-chain data availability. L2’s that use on-chain data availability are called rollups while L2’s that use off-chain data availability are called validiums or plasma.