Any object that does not allow light to pass through it.
An opaque material is something that light may not pass through.
"Opaque - not transparent or translucent; impenetrable to light; not allowing light to pass through." (Ref)
Examples of opaque objects:
- A metal water bottle
- A wooden desk
- A book
- A smartphone or tablet
- An apple
- A cardboard box
- A game controller
The list could go on... feel free to add any more you think of as a comment.