Blockchain networks are often described as permanent and unchangeable, but that does not mean the software running them stays the same forever. Like any complex technology, blockchains need to evolve. Developers discover bugs, new security techniques emerge, users demand better performance, and communities propose new features.

When you send cryptocurrency, the transaction usually does not appear in a confirmed block immediately. Between clicking “send” and seeing a confirmation, there is often an important intermediate stage: the transaction mempool.