Luminous objects are objects that can produce their own light, whereas non-luminous objects are the opposite: they cannot make their own source of light, and so rely solely on light from some other external source in order to be seen.
In fact, that is a major differentiating feature between the two: luminous objects can be seen because our eyes receive their light directly. Non-luminous objects, on the other hand, reflect light off of another source, and that reflected light is what enters our eyes for our vision.
An example of a luminous object is the Sun (a pretty big one, at that!). Through consistent fusion reactions wherein light hydrogen nuclei fuse to create heavier helium nuclei, it produces its own bright, fiery light.