IP66 is a designation for the so-called Ingress Protection (IP) rating, which indicates the resistance of an electronic device against the penetration of foreign objects and liquids. The abbreviation IP stands for "Ingress Protection". The first digit "6" means that headphones, a speaker, or a player are completely dust-tight, meaning no dust particles can get inside. The second digit "6" indicates resistance against powerfully jetted water. A device with this protection can therefore easily withstand, for example, heavy rain, rinsing under running water, or splashing water near a pool. However, it is not designed for immersion below the water surface.