The IP Code - or "International Protection Rating" -- is a global standard that specifies the level of protection that a specific electrical appliance provides against the intrusion of solid objects such as dust, falls and vibration, and water.
The numerals that follow the letters IP in a product's code (such as the JCB TOUGHPHONE's IP-54 rating) define the level of protection a device has been certified to provide. The first numeral indicates resistance to dust and dirt (solids) the second resistance to liquids. If a device's IP rating is not specified, you can safely assume it is not resistant to dust and moisture.
For more information, please see
The International Electrotechnical Commission's website. The IEC is organisation that develops and publishes international standards for all electrical, electronic and related technologies.