A single run of overhead track on which carriers (trolleys) travel.
An electrical railway in which a rail car or train of cars is suspended from or straddles a guideway formed by a single beam or rail. Most monorails are either heavy rail or automated guideway systems. (APTA1) A single rail on which a vehicle or train of cars travels. (DOI3)
Large format camera (usually, though there are medium format examples) constructed on an " optical bench " principle with front and rear standards on a rail.