A master node is a type of server present on the decentralized network and can be considered the warehouse of the blockchain, storing the whole of the blockchain. It is also known as the full node because unlike the other nodes in the blockchain, the full nodes contain the entire blockchain and not a fragment of it. This node contains everything about the blockchain network starting from the old blocks to the new blocks that are continuously being added.
Dash was one of the first crypto projects to have introduced master nodes at the beginning of 2017. This project allowed a return on investment (ROI) of about 47.5% of block rewards to the holder of the master node. There are many other crypto projects that have adopted the concept of a master node such as PIVX, Amsterdam Coin, Bulwark, and so on. The idea behind creating a master node was also to create a node that could accomplish several tasks which were beyond the capacity of the miners under the proof of work protocol.