Replace-by-fee (RBF) is a method that enables the substitution of an unconfirmed transaction with a new version that includes higher transaction fees. RBF was initially introduced in BIP125 and incorporated into Bitcoin Core 0.12.0 for implementation.
Different node software implementations result in variations in the rules governing Replace-by-fee (RBF). The most widely adopted RBF version today is the BIP125 opt-in RBF, implemented in Bitcoin Core 0.12.0. This version empowers transaction creators to signal their willingness to replace their transaction with a version that offers higher transaction fees.
An unconfirmed transaction has the potential to remain in a pending state indefinitely. This means that if there are other users willing to pay higher transaction fees, your unconfirmed transaction may never be included in a block and will remain unresolved.
If you find yourself pressed for time, you can broadcast a new transaction with higher fees. This new transaction is similar to the previous one but offers increased fees. When miners choose this transaction, they receive higher fees, making your transaction more competitive in the block space market. Wallets such as Electrum and Blockstream Green provide a convenient way to utilize Replace-by-fee (RBF) functionality for this purpose.
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