Learner's definition of DECORATION
1 : something that is added to something else to make it more attractive
a plain sweater knit without decoration
The handles are not just for decoration [=are not just decorative], they serve a practical purpose.
2 [noncount] : the act of decorating something (such as a room)
He's a genius at home decoration.
a unique style of decoration
She is certified to do interior decoration. [=interior design]
3 [count] : a medal or award that is given to someone for doing something brave or honorable (such as fighting bravely in a war)