The enclosure is the motor casing. There are different types of enclosures. These include open drip proof (ODP), totally enclosed fan cooled (TEFC), totally enclosed non-ventilated (TENV), and totally enclosed air over (TEAO).
Open drip proof motors have openings that allow air to flow through the motor to cool the windings. These are typically used in indoor settings.
Totally enclosed fan cooled motors have no openings to vent the windings. The motor is cooled by an external fan that blows air across the motor. These are usually used in dirty conditions.
Totally enclosed non-vent motors do not have a cooling fan and rely on the motor to dissipate the heat.
In a totally enclosed air over motor, the driven device provides the air to cool the motor.