Moisture-resistant plywood is typical for BWP or marine-grade plywood. It's meant to withstand the presence of water and withstand high humidity levels. These are made with waterproof adhesives and are given special treatment so as not to swell, warp, or rot, making them suitable for wet areas such as kitchens, bathrooms, and outdoor furniture.
Plywood is generally resistant to moisture, but the degree of its resistance varies by grade and treatment. Marine and BWP-grade plywood is suitable for wet conditions. Standard plywood will absorb some moisture and is likely to warp or swell and even rot when exposed to humidity or water for extended periods. If high levels of moisture are expected, then opt for moisture-resistant plywood.
Plywood does not endure moisture or MDF. While MDF does withstand some exposure to moisture, it becomes swollen and distorted and loses much of its strength once it is exposed to any form of humidity or water. BWP and marine-grade plywood types are significantly more robust than MDF for constructions using moistened or damp exposures. That is why plywood is much better suited to applications with much higher resistance to moisture, such as wet conditions.