Not all nodes on a blockchain network perform big operations, some are just there to perform simple to basic operations such as transactions authentication and validation. These nodes are referred to as lightweight nodes. Lightweight nodes join a blockchain network only to validate transactions and nothing more. They download blockheaders information which is just enough to carry out their functions and not a full blockchain on the network. Full nodes are the backbone of lightweight nodes and correct anything that goes wrong with them. Full nodes provide support as they verify any transaction against the blockchain core consensus rules.
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From @abdulganiy