Non-luminous objects are objects that cannot emit light on their own - as opposed to luminous objects that have their own source of light.
With this in mind, you can suggest an innumerable amount of examples of non-luminous objects, but let us stick to just two:
This one’s pretty obvious - unless you have a special textbook that lights up when you open it, it most definitely does not produce its own light of any kind. But then it is natural to ask: how do we see it?
To answer that, we have to understand the underlying principle of vision in general: all objects that we can see essentially reflect light from some other source into our eyes. The rods and cones underneath our retinas get triggered and send signals to the brain, and then it is up to our brain to put the puzzle pieces together and create an image - i.e. what we see.
So the book placed before you is doing just that: light from some source - maybe a lamp if you’re inside, or the Sun if you’re out and about - is falling on your textbook, and then reflecting into your eyes. After that, it's the brain that is doing it’s due diligence!
2. The Moon
Now this is a pretty interesting example, simply because of how the Moon appears to us at night: quite frankly, it always seems to shine. You may be inclined to ask how it does so, even though it doesn’t make its own light!
The truth is that the Moon is following the same principle as your Physics textbook: it too is reflecting light, but not from just any source - it is doing so directly from the Sun! That explains why it appears to be so bright at night, where there is no other astronomical light bulb interfering with its glow.
