There are such a variety of Cargo operations, ranging from national carrier ie: Lufthansa Cargo to dedicated Cargo outfit like Cargolux, Atlas..., the overnight parcels like DHL ,UPS, TNT.....and those operating on "behalf of", like EAT, Swiftair, Airatlantic,Cougar...., small outfit of only two aircrafts to giant fleet ie: FEDEX!!!
From oversize freight to mail service, from 747-400 to Cessna - Caravan not to mention the Airbus Beluga or the Antonov....
From assigned route coz of the relation between payload and sector lenght to "Ad Hoc" freighters
Like Dan and Lear mentioned, such a variety of jobs under one Name : CARGO
I started my carriere ....some years ago with a cargo company and had the chance to fly around and around the world.... but at an "interesting "altitude on DC-4 ,DC-6,ATL-98, type of equipment,and I learned a lot.....my ears are still ringing with the voice of the F/E yelling at me coz my rate of descent was too fast and the cylinder- Temperature was dropping !!!
Latetly I was flying exclusively at night 3 to 4 nights a week, 1 to 3 sectors per night on medium haul, with 2 to 4 days off at home.
I have left the Freighters just a few week ago, sadly not of my own will......
I'm gonna miss it