An elevator is a vertical transportation device typically used to vertically transport people and items between floors inside or outside a building. An elevator consists of an electric motor, a drive device, a control system, a car, car doors, a door operating system, and other components. 

The working principle of an elevator is to drive the wheel set to rotate through an electric motor, so that the steel wire rope or chain drives the car to move up and down. The running speed and direction of the elevator are controlled by the control system, and the opening and closing of the car doors are controlled by the door operating system. 

The types of elevators include: 

1. Passenger elevator: An elevator used for transporting personnel, usually installed inside buildings. 

2. Freight elevator: An elevator used for transporting goods, usually installed inside or outside buildings. 

3. Automatic escalator: a continuously running elevator, usually used for personnel transportation, installed inside or outside buildings. 

4. Automatic pedestrian walkway: a continuously running elevator typically used for personnel transportation, installed inside or outside buildings. 

The safety of elevators is very important because they are typically used for transporting people. Elevators typically require regular maintenance and inspection to ensure their safety and reliability. In addition, elevators also need to comply with relevant safety standards and regulations.