What are Nodes?
Cryptocurrency nodes are dedicated servers or machines just like the one you are using now that help distributes the cryptocurrency. Your computer can become nodes and help the network you're using, either Bitcoin or Ethereum, these networks rely on these nodes to run their resource-intensive applications that can't be managed by a single entity without an unacceptable loss of speed and efficiency.
Nodes are an essential part of the infrastructure of all blockchain-based networks. Each node has a full ledger of the transactions happening on the network and is able to independently verify the validity of transactions. Nodes collectively ensure that consensus is maintained on the blockchain regarding the correct ordering and correct history of transactions.
Decentralized applications rely on a distributed network of nodes to run their resource-intensive applications that can't be managed by a single entity without an unacceptable loss of speed and efficiency. Nodes are typically maintained by individual, independent parties. A 'node' is simply a computer running a program for which you can connect to the network, such as Bitcoin Core or the Ethereum Wallet app.
Almost all full nodes also help the network by accepting transactions and blocks from other full nodes, validating those transactions and blocks, and then relaying them to further full nodes. Most full nodes also serve lightweight clients by allowing them to transmit their transactions to the network and by notifying them when a transaction affects their wallets.
These types of nodes interact with the blockchain and depend on full nodes to provide them with the required information because they do not store a copy of the chain, they only check the current status for which block is last and broadcast transactions for processing. It is also called the Simple Payment Verification (SPV) node.
A master node runs the command and control center for blockchain networks. A master node is designed to run 24 hours a day.