The noun kilter means "balance," or "a state of working well," but you'll only find it in the phrase "out of kilter," meaning "not working right."
When things are off balance or out of whack, they're out of kilter, or off-kilter. If your bike keeps pulling to one side, or your toaster is only toasting one side of the bread you insert, they're both out of kilter. If you're studying hard and forgetting to eat well and exercise, you might also feel out of kilter. The word comes from the now-obsolete kelter, although the origin of this word is unknown.