A regular television is designed for use in dry areas, such as your living room or bedroom. They are not waterproof. The rear of the television is vented to allow for cooling, however, these vents will also allow moisture and condensation to accumulate inside the television. This can be extremely hazardous, with risks to the television shorting and potentially causing an electrical malfunction or fire.
The waterproof TV is a completely sealed design, engineered for use in wet areas. It is rated IP65 or higher and can withstand not only moisture, but also water from any direction.