Someone who is stouter is a little bit fat or heavy.
Being stouter is not bad, but it can make it harder to move around.
Examples:
The bear is stouter than the fox.
She is stouter than her sister.
The stouter man couldn't run as fast.
The stouter cat can't fit in the box.
The stouter tree is harder to push over.
The stouter boy can't jump as high as the others.