international standard IEC 60529 classifies the level of protection provided against the intrusion of solid objects (including body parts like hands and fingers), dust, accidental contact, and water. It consists of the letters IP (for "international protection rating"[1], sometimes also interpreted as "ingress protection rating") followed by two digits and an optional letter.

The digits ('characteristic numerals') indicate conformity with the conditions summarized in the tables below. Where there is no protection rating with regard to one of the criteria, the digit is replaced with the letter X.

For example, an electrical socket rated IP22 is protected against insertion of fingers and will not be damaged or become unsafe during a specified test in which it is exposed to vertically or nearly vertically dripping water. IP22 or IP2X are typical minimum requirements for the design of electrical accessories for in-door use. The standard aims to provide users more detailed information than vague marketing terms such as "waterproof".