What does IP mean?
 IP is the abbreviation of International Protection, also known as "Ingress Protection Rating", followed by the two numbers it is the protection established level, according to the international protection level certification IEC 60529, which represents "Solid particle protection " and "Liquid ingress protection".

About the two digits after the IP, the first represent "Solid particle protection ", commonly known as "dust protection rating", and the second is "Liquid ingress protection", that is "waterproof rating".

The following describes the difference about the digits:
The first digit is "Solid particle protection", which is used to indicate the ability of the product shell to protect internal components (such as electronic and mechanical parts) and prevent external objects from entering, unit number: 0-6, detailed description the following table:

IP rating	Effective against	Description
IP0X	-	No protection against contact and ingress of objects
IP1X	>50mm	Any large surface of the body, such as the back of a hand, but no protection against deliberate contact with a body part
IP2X	>12.5mm	Fingers or similar objects
IP3X	>2.5mm	Tools, thick wires, etc.
IP4X	>1mm	Most wires, slender screws, large ants etc.
IP5X	Dust protected	Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment.
IP6X	Dust-tight	No ingress of dust; complete protection against contact (dust-tight). A vacuum must be applied. Test duration of up to 8 hours based on airflow.

The second digit after the IP is "Liquid ingress protection", which indicates the ability of the device casing to resist liquid penetration, unit number: 0-9, detailed description is as follows:

IP rating	Protection against	Effective against	Details
IPx0	None	-	-
IPx1	Dripping water	Dripping water (vertically falling drops) shall have no harmful effect on the specimen when mounted in an upright position onto a turntable and rotated at 1 RPM.	Test duration: 10 minutes Water equivalent to 1 mm (0.039 in) rainfall per minute
IPx2	Dripping water when tilted at 15°	Vertically dripping water shall have no harmful effect when the enclosure is tilted at an angle of 15° from its normal position. A total of four positions are tested within two axes.	Test duration: 2.5 minutes for every direction of tilt (10 minutes total) Water equivalent to 3 mm (0.12 in) rainfall per minute
IPx3	Spraying water	Water falling as a spray at any angle up to 60° from the vertical shall have no harmful effect, utilizing either: a) an oscillating fixture, or b) A spray nozzle with a counterbalanced shield.  Test a) is conducted for 5 minutes, then repeated with the specimen rotated horizontally by 90° for the second 5-minute test. Test b) is conducted (with shield in place) for 5 minutes minimum.	For a spray nozzle: Test duration: 1 minute per square meter for at least 5 minutes[5] Water volume: 10 liters per minute (0.037 impgal/s) Pressure: 50–150 kPa (7.3–21.8 psi)  For an oscillating tube: Test duration: 10 minutes Water volume: 0.07 liters per minute (0.00026 impgal/s) per hole
IPx4	Splashing of water	Water splashing against the enclosure from any direction shall have no harmful effect, utilizing either: a) an oscillating fixture, or b) A spray nozzle with no shield. Test a) is conducted for 10 minutes. b) is conducted (without shield) for 5 minutes minimum.	Oscillating tube: Test duration: 10 minutes, or spray nozzle (same as IPX3 spray nozzle with the shield removed)
IPx5	Water jets	Water projected by a nozzle (6.3 mm (0.25 in)) against enclosure from any direction shall have no harmful effects.	Test duration: 1 minute per square meter for at least 3 minutes  Water volume: 12.5 litres per minute Pressure: 30 kPa (4.4 psi) at distance of 3 meters (9.8 ft)
IPx6	Powerful water jets	Water projected in powerful jets (12.5 mm (0.49 in)) against the enclosure from any direction shall have no harmful effects.	Test duration: 1 minute per square meter for at least 3 minutes  Water volume: 100 liters per minute (0.37 impgal/s) Pressure: 100 kPa (15 psi) at distance of 3 meters (9.8 ft)
IPx7	Immersion, up to 1 meter (3 ft 3 in) depth	Ingress of water in harmful quantity shall not be possible when the enclosure is immersed in water under defined conditions of pressure and time (up to 1 meter (3 ft 3 in) of submersion).	Test duration: 30 minutes.  Tested with the lowest point of the enclosure 1,000 mm (39 in) below the surface of the water, or the highest point 150 mm (5.9 in) below the surface, whichever is deeper.
IPx8	Immersion, 1 meter (3 ft 3 in) or more depth	The equipment is suitable for continuous immersion in water under conditions which shall be specified by the manufacturer. However, with certain types of equipment, it can mean that water can enter but only in such a manner that it produces no harmful effects. The test depth and duration is expected to be greater than the requirements for IPx7, and other environmental effects may be added, such as temperature cycling before immersion.	Test duration: agreement with manufacturer  Depth specified by the manufacturer, generally up to 3 meters (9.8 ft)
IPx9	Powerful high-temperature water jets	Protected against close-range high pressure, high-temperature spray downs.  Smaller specimens rotate slowly on a turntable, from 4 specific angles. Larger specimens are mounted in the intended position when being used, no turntable required, and are tested freehand for at least 3 minutes at a distance of 0.15–0.2 meters (5.9 in–7.9 in).	Test duration: Fixture: 30 sec. in each of 4 angles (2 min. total), Freehand: 1 min/m2, 3 min. minimum  Water volume: 14–16 liters per minute (0.051–0.059 impgal/s) Pressure: 8–10 MPa (80–100 bar) at distance of 0.10–0.15 meters (3.9 in–5.9 in) Water temperature: 80 °C (176 °F)

Quoted Material：Wikipedia