AIM Electronics 30-1004

the movement of air

the force per unit area that is exerted by a fluid upon a surface at rest relative to the fluid.

IP (or "Ingress Protection") ratings are defined in international standard EN 6529 (British BS EN 6529:1992, European IEC 659:1989). They are?used to define levels of sealing effectiveness of electrical enclosures against intrusion from foreign bodies?(tools, dirt etc) and moisture.