here's an answer I found so far but it's rather technical...

Masternode is a governing hub in cryptocurrency networks that requires initial collateral of tokens to operate.

Basically, a node is referred to any computing device that maintains a network. Cryptocurrency is supported by a network of computers, each keeping a digital record of the data called blockchain.

Further, a masternode votes on proposals to improve the Dash system and every masternode gets one vote. The special job of masternode includes creating instant transactions, called “InstaSend” and private transactions that hide that you’ve sent money, known as “PrivateSend.”

Here are some reasons why you should consider a masternode:

It enables instant transactions.
It enhances the privacy of the transactions.
It lets the user take part in governance and voting.
It facilitates the treasury and budgeting system in cryptocurrencies.

any better explanation than this?