The kinds of weakness intended here are:
• Lower narrator precision (خفیف الضبط): relatively less strength in remembering Hadith.
• An unknown narrator (مجہول): necessary information about the narrator is not clear to scholars. This does not merely mean a learner has not heard the name.
• An interrupted sanad (منقطع): the sequence is not connected: a narrator is omitted.
Even in these cases, the other transmissions must provide support that removes the weakness.