A quill drive is a mechanism that allows a driven shaft to shift its position (either axially, radially, or both) relative to its driving shaft. It consists of a hollow driving shaft (the quill) with a driven shaft inside it. The two are connected in some fashion which permits the required motion.
One example of a quill drive is found in a drill press where the quill allows the chuck to move up and down while still being driven.
Quill drives have been extensively used in railroad electric locomotives to connect between the traction motors and the driven wheels. The two are linked by a flexible drive which allows a degree of radial motion and possibly a small amount of axial motion. This smooths the drive from the motors and insulates them from shocks as well. Quill drives were used by many electric locomotives in the United States, particularly those of the Pennsylvania Railroad—their long-lasting GG1 design being perhaps the best known. Many locomotives built in France used quill drives as well.