Minecraft wiki entry for Quasi-connectivity, associated text: A piston activated by quasi-connectivity is sometimes described as "BUD-powered". However, quasi-connectivity and block update detectors (BUDs) are neither synonymous nor even subsets of each other. There are methods of QC activation that do not produce block update detectors (for example, any immediate QC activation method) and there are block update detectors that do not depend on quasi-connectivity (for example, stuck-piston BUDs).