Plasma is a highly complex scaling solution proposed by Vitalik Buterin and Joseph Poon in 2017. Basically, Plasma relies on Ethereum as the ‘root chain’ where subsequent parent chains and child chains — which are blockchains themselves — can be layered on top of it, increasing the processing capacity of the network.
OmiseGo is leading Plasma development on Ethereum, and their implementation is the first to launch on the smart contracts platforms.