A full node that keeps the full copy of the blockchain in real-time but has additional roles such as participating in governance and voting. On cryptocurrencies with masternodes such as DASH, they are a key component to the functioning of the blockchain network.
A temporary cache of transactions stored by a node that will exist until each transaction is incorporated into the blockchain. When users submit a transaction to the P2P network, each node receives and validates the transaction and, before rebroadcasting it to the rest of the network, keeps a copy of it in a local queue called a “mempool”. Once the transaction is included in a new “chained” block, the node first executes the transaction, updating the status of its copy of the blockchain, and then removes the transaction from its mempool.