The IP (Ingress Protection) standard is a system for classifying the degrees of protection provided by enclosures of electrical equipment.  For example a bathroom light fitting rated IP65 means that it is totally protected against dust and gives protection against water jets and water projected by a nozzle from any direction.

First numeral protection against human access or solid objects:

• 0 no protection.
• 1 Protected against solid objects with a diameter of 50mm and over (e.g. accidental insertion of hands).
• 2 Protected against solid objects over 12mm (e.g. jointed fingers).
• 3 Protected against solid objects over 2.5mm (tools).
• 4 Protected against solid objects over 1mm (small wires).
• 5 Protected against dust - limited ingress permitted (no harmful deposit).
• 6 Totally protected against dust.

Second numeral protection against harmful ingress of liquids:

• 0 no protection.
• 1 Protected against drops of condensed water.
• 2 Protected against drops of liquid.
• 3 Protection against rain.
• 4 Protection against splashing.
• 5 Protection against water jets.
• 6 Protection against conditions on ship decks. Water from heavy seas etc.
• 7 Protection against immersion in water. It shall not be possible for water to enter the enclosure under stated conditions of pressure and time.
• 8 Protection against indefinite immersion in water under specified pressure. It shall not be possible for water to enter the enclosure. ­