Moisture-wicking means the sweat is moved through tiny spaces within a fabric due to the molecular forces between the liquid and the fabric’s internal surfaces.
Brands refine this process by carefully engineering the yarns' structure within their fabrics and applying various treatments to surfaces within that structure.
Synthetic fabrics are “hydrophobic,” which means they resist the penetration of water, or in other words, they are waterproof. That’s why you see a lot of synthetic fabrics, like polyester or nylon, excel at moisture wicking.
The two terms, moisture-wicking and waterproof, may not be the same thing. However, one is closely related to the other.