What Is the Concept of “Minimum Transaction Fee” in Some Cryptocurrencies?

A minimum transaction fee is a protocol-enforced or node-policy-enforced lower limit on the fee rate for a transaction to be considered valid or relayed. While the underlying protocol may allow zero fees, network nodes often enforce a minimum relay fee to prevent spam and resource exhaustion.

If a transaction falls below this minimum, nodes will typically reject it from their mempool and refuse to broadcast it to the wider network. This creates a baseline cost for utilizing the blockchain and ensures a minimum level of compensation for miners' work.