CAD, or Computer Aided Design, is a tool used in many different industries to describe plans, parts, assemblies, systems, circuit diagrams, chip design and so on. CAD was once a very specialized and expensive proposition, requiring heavy duty computers and peripherals like pen plotters and digitizing tablets. But that was a long time ago, and now CAD can run effectively on lowly laptops, though it still helps to have a beefy machine and good graphics card if you expect to do anything serious. Even so, the CAD program is likely to be more expensive than the computer that you choose to run it on.
You are likely to run into meshes that come from CAD systems from time to time. Architecture, engineering, aerospace and automotive use CAD exclusively, and other disciplines like product design are doing so as well. That said, applications like Cinema 4D are also often used in these disciplines, and its common to see both in use by design teams across the board. That is one of the reasons why Cinema 4D can read and write several of these formats, such as DXF.