Second best is used to describe something that is not as good as the best thing of its kind but is better than all the other things of that kind. He put on his second best suit
You can use second best to describe something that you have to accept even though you would have preferred something else. He refused to settle for anything that was second best. Second best is also a noun. Oatmeal is a good second best. something that you have to accept which is not perfect or not the best. not quite as good as the best one