You can see things when light from them enters the eye. When light starts from the thing, that thing is called a luminous source. The Sun is a luminous source because light comes from it. Car headlamps, torches, and candle flames are also luminous.
You can still see things when the light does not start from the thing. Light from a luminous source reflects from the thing, and your eye detects this reflected light. Now the thing you see is referred to as a 'non-luminous'.
Many everyday things are non-luminous sources. The table, a chair, the curtains, and that dog are all examples.