The only thing I've ever seen "IP" stand for was inch-pound. It's used to distinguish things like ASHRAE books using Imperial measurement from ones using metric measurement.
In the electrical power field, IP stands for Ingress Protection rating. It refers to the ease or difficulty that water, dust, fingers etc would have in getting into electrical equipment. The US equivalent is the NEMA rating.
RiBeneke is correct, refer to EN 60529. This will tell you how to select and test to show you conform to IP requirements. Christopher Caserta
Sr. Regulatory Engineer
ccaserta@enorthhampton.com
Ph:904-225-0360
Fax:904-225-0340