When photography and the photographic process was in its infancy the light sensitive material coating on (usually) a plate of glass had to be used immediately after application, ie. while it was still wet. This obviously had many drawbacks and it was only a matter of time before the early pioneers of photography developed a new process whereby the light sensitive coating was dry in use. This far more practical and versatile system became known as the Dry Plate process.
In this modern digital age the photographic plate has been replaced by an array of light sensitive diodes which record the image, this step is arguably analagous to the advances made by the early pioneers.