Plasma is a scalability solution specifically designed for the Ethereum blockchain. It's a layer-2 scaling solution that aims to increase transaction throughput by creating child chains that operate independently from the main Ethereum chain. These child chains can process transactions more efficiently, and only periodically submit summaries of their activity to the main chain ¹ ².

In essence, Plasma helps reduce the load on the Ethereum mainnet by moving computation and storage off-chain, making it a useful solution for transactions between arbitrary users. However, it's worth noting that Plasma has its limitations, such as delayed withdrawals and potential data availability issues ².