Most rainwear on the market is water-resistant and not waterproof. A waterproof coat would be made out of a material such as vinyl and would not be breathable and would cause the wearer to sweat.
The water repellency of fabric is measured in pounds per square inch (psi). Water resistancy of a fabric is determined by a water pressure test. The higher the psi, means the more water the fabric can repel before having water pass through the fabric and getting the wearer wet. Fabrics such as Gortex have a very high psi rating and will be more expensive than fashion wear raincoats. Not all raincoat fabric has a psi number.
Raincoats that are not waterproof, but are water resistant are treated with a durable water repellent (DWR), think Scotch Gard Fabric Spray. Over the lifetime of the coat the water repellent coating can break down and will need to be revived.