The phrase "to knock out" means to render someone or something unconscious, inactive or unable to perform a task. It can be used both literally and figuratively. For example, if you get hit hard enough, you could say that you were "knocked out," meaning you lost consciousness. In boxing, when one fighter knocks the other down, it is said they have "knocked them out." Figuratively, someone might use this phrase to describe a successful performance or achievement: for instance, saying that their team won and "knocked out" the competition.