Connected Chain of Transmission (اتصال السند):

A chain of transmission which is connected without interruption in such a manner that it is logically acceptable that the succeeding narrator received the hadith from the preceding one. Therefore, there should be no gap, whether in time or place, which may make their meeting impossible.

Disconnected Chain of Transmission (فقد اتصال السند):

A chain of transmission which is interrupted in such a manner that it is not logically proved that the succeeding narrator had received a hadith from the preceding one.