The art and science of photography -- which literally translates as "drawing with light"-- evolved throughout the 19th century. Early practitioners discovered chemical compounds that would darken when exposed to light, and others that would stop this darkening, and "fix" or make permanent an image. A number of processes built on these discoveries, including cyanotype, salted paper printing, Van Dyke Brown, albumen, calotype, platinotype, and many others.
As photography developed (pun intended) through the silver gelatin process and on into the digital realm, many photographers have come to appreciate the craftsmanship and beauty of these processes, and began returning to the roots of photography. We learned how to mix light-sensitive chemicals and apply them to metal, glass, and paper as our "ancestors" did, and in a wonderful melding of old and new, discovered how to use images made on digital cameras and even iPhones can be used to make negatives.
They are called "Alternative Processes," and when comparing them to modern film and digital imaging, they certainly are an alternative. But I like to think of them as "Historic Processes," since they are the foundation upon which the modern methods of producing photographs is built.