IP is an acronym "Ingress Protection" and is a ratings standard used to indicate the level of protection an enclosure for electrical equipment gives against solids and liquids. It is a measurement of the protection an item will have against solid objects (dust, sand, dirt, etc.) and liquids.
An IP rating is comprised of 2 numbers. The first number refers to the protection against solid objects (dust, etc) and the second number refers to protection against liquids.
Each IP rating has two numbers, both of which give you information about the protection level. A higher number means greater protection against solids and liquids.
Take a look at the chart below to better understand the protection offered with each number.
With an IP65 rating, an item can be used in an outside setting and are water-resistant but they are not water-proof and are not suitable to be submerged.