From my experience, water resistant means that the item will survive a splash of water but not any form of prolonged exposure.
Water proof suggest that it is
Impervious to or unaffected by water.
For waterproof items, there is often an IP number provided which helps you understand the level of waterproofness the item offers.
IP codes are widely used in the industry.
For example, a E+LITE from Petzl is rated as IP67 per the manufacturer. IP67 means you can expect the light to work if it is submerged in water less than a meter for no more than 30 minutes.
For outwear such as jackets, the bigger issue is that if your jacket is fully waterproof, you will end up wet from your own sweat. The balance between breathability, waterproofness and longevity of the material are all equally important factors in this case.