more specifically it is a render made by a 3d imaging program called cinema 4d. The are generally semi transparent in nature and are used to enhance the background in an image. They are sometimes hard to blend into an image. Some of the signature artists in this forum may be able to give you tips in blending them.
The most prolific use of c4d's are in signatures but i have seen them used in great artworks. Some people say that using c4d's is a form of cheating but i strongly disagree. I feel that artists should use every tool at their disposal to portray their feelings and the meaning of what they want to convey to the viewers.
Good luck and best regards,
chad