A node is part of a blockchain that communicates with other nodes.
Every computer that contributes to maintaining a Proof-of-Work blockchain is called a node. Nodes are not the same as miners, because nodes do not do the difficult calculations that miners do. Nodes only store the blocks. This requires less strong hardware, so normal computers can also be a node. On the other hand, nodes do not receive rewards like miners. For this reason, nodes are mainly run by enthusiasts and hobbyists.
A miner must always run an entire node to select valid transactions to form a new block. If it does not have a full node, it cannot determine which pending transactions are or are not valid. If a node cannot verify that the balance (on the blockchain) matches the transaction, it cannot execute a transaction.
At the same time, a miner is always a full node. A node is not necessarily a miner, a node is just a recipient and sender of blockchain data. A full node has a complete copy of the blockchain transaction history.
Proof-of-stake blockchains also use nodes. An important difference is that there are therefore no miners at PoS. A number of POS blockchains also include so-called master nodes. A masternode is generally heavier than a regular node. In addition to validating and sending transactions, it also always does other things on the side. For example, when a voting takes place, it is usually maintained by a masternode. Masternodes only exist with PoS blockchains.
The biggest difference lies in the size of the memory and the power, which is many times higher in a masternode. In general, a masternode is also always online. In most cases, this does come with a reward, but this also depends on which cryptocurrency a masternode is running for.
