iPhone X has rating under IP67 under IEC standard 60529. The number 6 in your rating represent the degree of dust protection from your phone. The rating ranges from 0 to 6. The second number that is 7 represents the degree of moisture protection. The rating range of protection level ranges from 0 to 8. It simply means that iPhone X is having highest level of protection of phone from moisture and dust.
You can submerge the device up to 1 meter for almost 30 minutes. Apple does not offer warranty for liquid damage. It means that you must avoid taking the phone for swimming, shower or any water activities. It is safe to take the iPhone in light rain, but make sure that it is safe from accidental drops and spills.
Below is the fineprint from Apple:
“iPhone X is splash, water, and dust resistant and was tested under controlled laboratory conditions with a rating of IP67 under IEC standard 60529. Splash, water, and dust resistance are not permanent conditions and resistance might decrease as a result of normal wear. Do not attempt to charge a wet iPhone; refer to the user guide for cleaning and drying instructions. Liquid damage not covered under warranty.”