Put two objects next to each other and they're juxtaposed: placed side-by-side to emphasize their contrast. An art exhibit might have the paintings of one period juxtaposed with those from another to emphasize how different the two periods were.
The word juxtaposed comes from the Latin juxta, meaning "next" and the French poser, meaning "to place." When two objects are juxtaposed, they are placed next to each other, or side-by-side for comparison. It doesn't just have to be objects. After a guest manager's style was juxtaposed with your normal manager, you decided to look for a new job.