Types of Nodes:

Full Node: Has downloaded and verified the entire blockchain.

Currently 750GB

Pruned Node: Has downloaded and verified the entire blockchain, but has discarded older transactions to save disk space.

Typically 250 GB

Lightweight Node: Has downloaded a copy of the UTXO set, a full list of spendable coins. An attached wallet needs this to check the validity of a proposed transaction. This is not fully verified until it is broadcast on the Bitcoin network, where full or pruned nodes can confirm this transaction.

Currently 12GB, has grown from 4GB since Taproot launched in November 2021.

This is a major discussion point in the OP_RETURN debate