IP67 is two numbers, one that refers to the dust resistance rating and one that refers to water resistance. IP6x is the highest dust resistance rating, so the iPhone X is fully protected against dust.
IPx7, the water resistance rating, means the iPhone X can withstand immersion in water up to one meter (3.3 feet) for 30 minutes, tested in laboratory conditions. IPx7 is the second-highest rating, below IPx8, which indicates an ability to withstand long periods of submersion under pressure.
Apple's iPhone 8 and 8 Plus are also rated as IP67 water and dust resistant. With all of its devices, Apple warns that while they are water and dust resistant, those are not permanent conditions and resistance could decrease as a result of normal wear.
Because Apple does not cover any kind of water damage to iOS devices, it's best to continue to use caution when exposing a water resistant iPhone to liquids, avoiding contact whenever possible.
There were rumors suggesting Apple's new iPhones might feature an IP68 water resistance rating to match the Samsung Galaxy devices, but that particular rumor did not turn out to be true.
As for the Apple Watch Series 3, it too has identical water resistance ratings to the Apple Watch Series 2. According to Apple, the Apple Watch Series 3 has a water resistance of rating of 50 meters under ISO standard 22810:2010.
The Apple Watch Series 3 is suitable for shallow-water activities like swimming in a pool or an ocean, but it should not be used for scuba diving, waterskiing, or other activities that involve exposure to deep water or high-velocity water, including a shower.