The Ingress Protection (IP) Rating is a safety rating published by the International Electrotechnical Commission (IEC). The equivalent European standard is EN 60529. It classifies and rates the degree of protection provided by mechanical casings and electrical enclosures against intrusion, dust, accidental contact, and water. The higher number the better protection.
The first digit indicates level of protection that the enclosure provides against access to hazardous parts, and ingress of solid foreign objects. On a scale of 0-6, with 6 being completely sealed against dust. It’s not impossible for dust to get into the device, but it won’t get into device in an amount to cause damage.
The second digit indicates protection of equipment inside the enclosure against various forms of moisture (drips, spray, submersion etc.) On a scale of 0-8, rating 1 and 2 use dripping water, and should keep device safe with minor spill. Rating 3-6 water sprayed onto the device at varies pressure for varies length of time. For rating 7, the device can be submerged at 3 feet for 30 minutes, and rating 8 is submerged up to 13 feet.
The digit 0 is used where no protection is provided.