Escalator is a common name for a mechanical apparatus in the form of a moving stairway, the steps of which ascend or descend, carrying passengers from one floor to another of a building.
The earliest type of escalator, patented in 1891 by Jesse W. Reno, was in the form of an inclined conveyor belt destined for industrial use. In 1899, Charles D. Seeberger joined the Otis Elevator Company, bringing with him the name escalator (which was created by joining scala, which is Latin for steps, with elevator). The Seeberger-Otis union produced the first step-type escalator made for public use, and it was installed at the Paris Exhibition of 1900, where it won first prize. Mr. Seeberger eventually sold his patent rights to Otis in 1910.

The Landing
The floor plates are level with the finished floor and are either hinged or removable to permit access to the machine spaces under them.

The comb plate is the piece between the stationary landing and the moving step. It slants down slightly so that the comb teeth fit between the cleats on the steps. The front edges of the comb teeth are below the surface of the cleats.

The Truss
The truss is the mechanical structure that bridges the space between the lower and upper landings. The truss is basically a hollow box made up of two side sections joined together with transverse braces across the bottom and just below the top. The ends of the truss rest on concrete or steel supports.

The Tracks
The track system is built into the truss to guide the step chain, which pulls the steps through an endless loop. There are two tracks: one for the front of the step (called the step-wheel track) and one for the trailer wheel of the step (called the trailer-wheel track). The relative position of these tracks causes the steps to appear from under the comb plate to form a staircase, and disappear back into the truss.

The reversal track at the upper landing rolls the steps around the top and starts them back in the opposite direction. An overhead track ensures that the trailer wheels remain in place as the step chain is turned back on itself.

Source : Encarta encyclopaedia and Otis Elevator Company.