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.
outdoors.stackexchange.com/users/1902/ppl
"Waterproof" means that no water will penetrate.
"Water resistant" means that there exists a limit of exposure at which water will penetrate.
Watches are normally water resistant to a particular depth below which the water pressure is too high and the seals are breached.
Breathable clothing quite of often states some comparable metric indicating, for instance, the weight of water which would be required for water to penetrate the fibres.
The problem with the terms is that there is no regulation and so we might buy a rain jacket and call it "a waterproof" even though it is not.
Some manufacturers will also state that an item is waterproof to some limit, which is confusing.
What you need to look for a test that has been performed or something stating limits.
outdoors.stackexchange.com/users/2611/stevemarvell
I'm not a native speaker, but being waterproof suggests more endurance to water than being only water-resistance.
But linguistic nuances doesn't make law.
More important is, what are the norms and regulations about using such definitions, in the country where that equipment is produced or sold.
If there are such regulations, false promises may make manufacturer liable, if there are no regulation, anyone can sell anything under any name, and all such names are meaningless.
When it comes to norms, there are the ISO norms that define water resistance - see the Wikipedia article .
The article mentions, that the term waterproof is not defined in the ISO norms, and therefore it should not be used.
So buying water resistant gear you should check 2 things:
is there a water resistance rating compliant with ISO norms is the producer and manufacturer a stable corporation registered in country, which protects customers from companies giving false information in product description
outdoors.stackexchange.com/users/557/Danubian Sailor
In outdoor garments, water resistant means that it will keep you dry in light rain for some time, is not a garment to withstand heavy rain.
Water proof means that it will keep you dry in the rain, but then it depends on the quality of the material, and how well is designed.
outdoors.stackexchange.com/users/11760/Steven
Water resistant is often used where water resistance is quantified usually in terms of static pressure head.
An obvious example is watches which have long been classified by water depth in metres of pressure in bars or atmospheres.
Also fabrics for jackets, tents etc will be specified by the head of water which they will resist.
In many ways a specified level of water resistance is more useful than just 'waterproof'.
Waterproof is generally used for clothing and means that it won't be penetrated by rain, this is also complicated by the fact that breathability is also very significant in terms of keeping dry.
Similarity
some fabrics, like ventile , have some overall performance advantages in some circumstances in terms of durability, breathability and comfort.
Equally there are systems like Buffalo which focus on overall warmth and comfort rather than absolute waterproofing.
outdoors.stackexchange.com/users/8820/Chris Johns
I've gone camping for quite a bit, but when it comes to choosing between water resistant and waterproof gear, I always take the latter.  I'm actually curious if there's a difference between these two terms.  For me, water-resistant always sounded like some cheap marketing gimmick to make the product seem waterproof.  Is there any actual "real" difference?
What's the difference between water-resistant and waterproof?
outdoors.stackexchange.com
<waterproofing><waterproof-clothing>
outdoors.stackexchange.com/questions/4750
outdoors.stackexchange.com/users/2285/yuritsuki
Water resistant means that there exists a limit of exposure at which water will penetrate.  Water proof  suggest that it is   Impervious to or unaffected by water.  Waterproof means impervious to rain and implies greater endurance than water resistant, which has a limit.
Water resistant means a limit to exposure. Waterproof means rain will not penetrate and it has more endurance than water resistant