Plasma is produced to be a scaling solution technique specifically for Ethereum. What it aims at being is to work as a framework for side chains. Acting sparingly with the main chain, (the Ethereum blockchain), it is arranged in a hierarchy that bears a number of “child chains” produced on top of the main chain.
The Plasma frameworks are created through utility of smart contracts and Merkle Trees. What this allows is the production of side chains that are unlimited in number. Such are smaller reproductions of the Ethereum blockchain.
Simply, Plasma is an off-the-main-chain solution that aims at increasing the efficiency of the Ethereum network through the acquisition of bulk processing duties from the main chain and effectively redistributing it across smaller, working chains.
While it had been initially created for the Ethereum blockchain by Vitalik Buterin and Joseph Poon in August 2017, the Plasma solution went on to become compatible with other blockchains.