To keep it simple IPX5 is resistant to a low-pressure water streams like the one flowing through a typical home tap, from any direction.
Read on to understand these ratings in depth.
Many Headphone Manufacturers are advertising their products as "Dust resistant", "Sweat-resistant" or "Splash resistant".
To be more credible to their claims, they specify "IP Codes" stating their Water Resistance Rating.
IP stands for "Ingress Protection". It measures how well a device is protected against both solid objects and liquids.
IP ratings look something like this IPX4, IPX5, IPX7... and so on.
IP ratings are only given to a product that undergoes special testing by a certified, independent company.
So no company can just use their own IP rating on any product, just because they feel like it's worth it.
(Thank God for that. That would have made things really messy)
Even though the manufacturers tend to highlight that their product is "Waterproof", you shouldn't be fooled.
As far as IPX5 rating is concerned, it protects your device from just low-pressure water streams like the one we have from the taps in our homes. You cannot and should not test by submerging the device into water or putting it through running water though.
Most probably you'll lose your device in that case :)
If you would like to read more about IP Ratings, check out this article about IP Codes on Wikipedia.
Or if you're into learning things in entertaining ways, check out this video.