Firstly, here are definitions from Oxford English Dictionary:
Water-proof means impervious to water.
Water-resistant means able to resist the penetration of water to some degree but not entirely
Comparing to water-proof, water-resistant is the lower level of water protection. Some water-resistant devices always have some special design to fight with water and make it difficult for water to enter. This is always use in devices like watches to help them survive from hand washing or raining.
The first number after letters “IP” shows it solid protect, which is measured form 0 to 6, while the second number is the degree of protection against the entry of moisture, the rage is from 0 to 8. To transfer these two numbers to the meaning we understand, you can follow two charts below: