A "waterproof seal" refers to a barrier or closure that prevents water from passing through. It is a way to keep something protected and dry when it comes into contact with water. Full definition
This is not the strongest waterproof seal on the market, but works well for aquatic sports and tends to be more comfortable than other seals. (geekwrapped.com)
This type is looks more natural and perfect to apply at our home, but if we want to use unfinished hardwood we need to apply proper waterproof seal during installation. (decorationchannel.com)
The headphone socket automatically seals itself, while the memory, removable battery, and SIM slot are under the back cover, which can still be pulled off like the regular S 4, but now has waterproof seals around the edges. (slashgear.com)