What do the scholars of Hadith mean when they say about a narrator that he is "matrook" (abandoned)?

The "Matrook" (abandoned) is a category of discreditation among Hadith scholars, referring to a narrator accused of lying, whose narrations people have abandoned. For a narrator to be considered "Matrook," it is not sufficient for only some people to accuse him of lying; rather, everyone must agree to abandon his narrations. If it is established that a narrator is "Matrook," then his narrations are discarded and not relied upon.