International Protection Marking (IP) Codes
You may be starting to see something called "IP codes" in the specifications of radios (and a rapidly growing number of cell phones) you buy. The "IP" stands for "International Protection", sometimes interpreted as "Ingress Protection". The IP code was created by the International Electrotechnical Commission (IEC), a non-profit, non-governmental organization that creates international standards for all sorts of “electrotechnology,” from semiconductors to batteries to home appliances to…your ham radio.
The code is officially known as IEC 60529, "Degrees of Protection Provided by Enclosures (IP Code)" and was adopted in the U.S. by the American National Standards Institute (ANSI) as ANSI/IEC 60529.
The IP code has two numbers. The first number (0 - 6) indicates your device’s protection level against “solid particles,” which includes everything from large body parts to microscopic specks of dust. An IP2X rating, for example, means that your device is protected against “fingers or similar objects,” but anything smaller than a human finger might be able to get through and do some damage. An IP rating of IP6X, on the other hand, means that your device is dust-tight, and even tiny bits of dust won’t end up inside the casing.
The second number indicates your device’s protection level against liquid—specifically, fresh water. This number ranges from 0 to 9K, though no consumer product is rated 9K (or 6K, for that matter). So the highest rating you’ll see here is an 8, which means the device can be immersed in water that is deeper than 1 meter—but the actual depth level is determined by the manufacturer, as is the amount of time the device can be immersed.
The IP ratings for liquid protection are not cumulative beyond IPX6. This means that any device rated IPX7 or IPX8 only had to pass one test (the test that determined its number), not any of the other tests. So while an IPX7 phone has passed a test where it was fully immersed in up to 1 meter of water for 30 minutes, it hasn’t necessarily passed the IPX6 test or the IPX5 test, both of which involve water being projected by a nozzle or powerful jets. In other words, your IPX7 phone might be fine if you drop it in the pool, but could be compromised if you spray it with a hose. (Of course, it could also be fine if you spray it with a hose—the point is that the IP rating alone doesn't tell you.)
In addition, the liquid protection ratings address pure fresh water only. They don't consider other liquids ( e.g., oil or a spilled soft drink) or contaminants within the water, such as chlorine (e.g., in a pool) or salt (in the ocean) that may have corrosive or other damaging effects. If you drop your phone in a liquid that’s not fresh water, you can (and should) rinse it off with fresh water before setting it aside to dry. Further, the IP rating only tells you how protected your phone is against dust particles and pure water—not how protected it is against other environmental factors, such as extreme temperatures, vibration and mechanical impact (e.g., dropping it).
Other Ingress Protection Standards
Two other standards concerning ingress protection are NEMA standard 250, “Enclosures for Electrical Equipment (1000 Volts Maximum)”, from the National Electrical Manufacturers Association; and the United States Military Standard MIL-STD-810, Environmental Engineering Considerations and Laboratory Tests. The ratings between these two standards are not directly equivalent with each other, nor are they equivalent with the IP Codes. In addition, these standards require additional product features and tests (such as functionality under icing conditions, enclosures for hazardous areas, "ruggedized" construction, knock-outs for cable connections and others) not addressed by IP ratings. See the Sources and Links below for more details
Sources & Links:
What those IP ratings like IP68 or IP53 really mean. by Sarah Jacobsson Purewal/techConnect.
IP Code. from Wikipedia.
International Electrotechnical Commission, description on Wikipedia.
NEMA Enclosure Types; a summary of the the definitions of NEMA Enclosure Types (PDF, 238 KB)
MIL-STD-810; description on Wikipedia.