Modern photographers use methods that were unavailable or extremely difficult before the advent of digital cameras.  Among them is the ability to seamlessly combine multiple images into a single photograph.  The term composite is used to describe the picture that results from combining any two or more images in some creative way.  There are no rules; it can be any mashup of scenes to meet any artistic goal.  

Cutting and pasting a subject into a lunar landscape is an example of a composite.  An early tool to do this was Adobe Photoshop.  With our common linguistic practice of verbizing nouns, we now have the term “Photoshopping” to describe the making of fictitious or synthetic scenes.

Because digital compositing can easily create any such pictures, it is often used to deceive the viewer.  But there is a special case of compositing that has a different goal.  When the individual images are taken by the same camera through the same lens, looking at the same subject, it is called a “blend”.  The purpose is not to deceive, but to better represent the appearance and feeling of the scene by combining pictures taken at different moments.