Firstly it’s worth noting that there’s a difference between being waterproof and water-resistant. Waterproof means something is impervious to water regardless of how long it is submerged, water-resistant means a product can stop water entering it to some degree, but not entirely. When we’re talking about waterproof connector it’s almost always about how water-resistant they are where they are used. They can’t survive in water indefinitely.
IP is the name of the standard that was drawn up by the International Electrotechnical Commission (IEC) to determine how resistant an electrical device is to fresh water and common raw materials – like dirt, dust and sand.
The first digit after IP is the rating the IEC assigned a unit for its resistance to solids. In this case, it’s six – which means no “harmful” dust or dirt seeped into the unit after being in direct contact with the matter eight-hours.
Next, we have the water resistance rating.
There are two leading ratings at present – seven and eight, with the former meaning that the device can be submerged in up to one meter of fresh water for half an hour, and the latter up to 1.5 meters for half an hour. Both are resistant to dust.