For materials and products to be considered waterproof, they need to meet a specific criteria. This criteria includes the amount of water pressure (psi) they can withstand before leaking or an "mm/24 hours" rating which equals the amount of rainfall a fabric can withstand in a single day before water starts to leak through.
In footwear terms, to be considered waterproof they will most likely have a barrier or membrane build inside as well as fully sealed seams and stitching, designed to keep water out and ensure feet stay dry.
Water repellent products on the other hand, have a coating or finish that is not easily penetrated by water but is still difficult to protect stitching and the tongue area.
All products from the Waterproof range have a waterproof breatable membrane which is pressure tested in production to guarantee your feet stay dry when working in wet environments.