A pantograph is a series of arms connected in a special manner such that they move in a fixed relationship to each other.
The first pantograph was constructed in 1630 by Christoph Scheiner, who used the device to re-create diagrams. One arm contained a small pointer while the other held a drawing implement, and by moving the pointer over a diagram, a copy of the diagram was drawn on another piece of paper. By changing the positions of the arms in the linkage between the pointer arm and drawing arm, the scale of the image produced can be changed. Modern copies of the same device can be found in many toy stores.
Another common use for the pantograph was to construct "drafting machines". In these devices the arms were arranged in such a fashion to keep the "pen" arm at a specific angle in relation to the "pointer" arm - although the pointer and pen are missing. The "pointer" arm is fixed to the side of the table at a right angle, implying that that "pen" end is likewise at a fixed right angle no matter where it is moved. Typically a straight-edge is placed at the "pen" end, which can then be used to quickly draw a series of parallel lines. Drafting machines replaced the older system of t-square and triangles, speeding up drawing.
Another use for the term refers to the arms that collect current from overhead lines on electric trains or trams. They set up standing waves in the wires which can degrade current collection. This means that on some systems adjacent pantographs are not permitted.