User-Activated Soft Fork (UASF)

A User-Activated Soft Fork (UASF) is an update or change to the Bitcoin network’s protocol initiated by users or nodes, who integrate new code into their Bitcoin implementations and demonstrate their acceptance of the change so that miners and other users can implement the same changes knowing they will maintain consensus. Since the update is a soft fork, updating is not required, because the changes to the protocol are backwards compatible. If a node does not update, they are not harmed at all.