EIP-1559 stands for Ethereum Improvement Proposal 1559. It is a proposal for upgrading the Ethereum network to improve the efficiency of network transactions by introducing a hybrid system of base fees and tips. Under EIP-1559, a base fee is algorithmically determined as the price that all Ethereum users would pay for transaction completion. Tips, on the other hand, are optional fees that users can include to expedite their transactions. EIP-1559 was implemented in August 2021 with the objective of reducing transaction costs and enhancing the overall user experience on the Ethereum network.