Excellent! We can clearly see that the rubber band's shape is changing. And, from common sense, we know that the rubber band is a solid.
The rubber band's shape changes because we are pulling it. The rubber band doesn't change its shape by itself. Also, the rubber band tries to return to its original shape once we stop pulling.

So, that is the important aspect about solids: even if their shape changes due to an external force, they try to return to their original shape.