IP means: International Protection and applies to the item’s enclosure.
IP is indicated along with 2 digits, (i.e. IP20) to state how safe the item is as regards the ingress of dust, solid objects and water. The first digit always indicates the degree of protection against foreign matters penetrating the product, but at the same time, it indicates a certain minimum degree of protection against contact with hazardous components. The second digit indicates the degree of protection against water penetrating the material.
Yes (except for those with integrated LED) if the size of the light bulb allows it to be fitted in the lamp. It is the physical size and not the Watts in the light bulb that determine whether you can fit it in the lamp when it comes to energy-efficient light bulbs.