C4D is the file format generated by the Cinema 4D program, a 3D graphic modeling and rendering program. This program lives up to the "Cinema" part of its name by being widely used in the movie industry, used in making graphics for films from Chronicles of Narnia to The Polar Express. Just what is the fourth dimension that is referred to in its name is less clear. It is a proprietary commercial program published by Maxon.
Cinema 4D had its origins in a ray-tracing program for the Amiga that won a programming contest for its authors, Christian and Philip Losch. It was developed into a full-fledged 3D art program, for the Amiga at first and later for other platforms including Windows and MacOS. In the past there were a number of different editions aimed at different markets, but as of version R21 in 2019 there is a single executable with all functionality, though some functions might be limited for some users depending on licensing.