A Monorail camera is a type of view camera. They are large format models that come with a front standard to hold the lens along with a rear standard with the ground glass and film holder. They can use 120 or 220 roll film along with various sizes of sheet film.
The camera also has a bellows to exclude light. Both of the standards allow for extensive movement and are attached to a solid metal rail or girder. They can be moved along the rail or girder for focusing purposes. The various sections can be moved along the rail or girder to accommodate add-on components or accessories, to adjust focus, etc.
Monorail cameras are usually bulky and heavy and can weigh more than 30 lbs, but they have great flexibility and almost unlimited camera movements such as swing, tilt, shift, and rise and fall. The front and rear standards can be adjusted separately.
Some models are made in modular fashion so different parts such as standards, bellows and extension rails can be easily attached or taken out. These cameras are popular with studio and industrial photographers as they can handle radical adjustments or elaborate accessories. Good monorail cameras usually cost a few thousand dollars.