Have you seen people using the aerial platforms that rise up vertically, for lifting weights or reaching higher places? To lift heavy goods in a warehouse or to reach the bulb in a street light? The device used is called a scissor lift.
It is called a scissor lift because the X pattern mechanism used is called a scissor mechanism. The top of this machine is a platform where one can stand or store goods. The platform is then raised slowly using mechanical power. Once the job is done, the platform is descended using the same mechanic energy or hydraulic energy.
When hydraulic mechanism is used, the pressure is released and the platform comes down to its position. This method is more preferred as not much power is used and in case of a malfunction, one has to just release the valve and the platform is returned to its position safely. A problem in the mechanism will not affect the descent of the platform.