A scene is defined as the 3-dimensional digital space in which all elements needed to create digital images are assembled; models, lights, cameras, etc.
Below is an example of a simple scene used for a studio shot, showing a sofa against a simple bent plane to create a soft background. Also visible are the lights and cameras to render images from different viewpoints.
Example of a simple scene used for a studio shot.
Essentially, it is the digital equivalent of a studio or room in which a photographer will place a product, set lights and position his camera.
A scene could hold anything from a single model and a light to a fully decorated interior, to an entire cityscape, or even a planet.