A hadith is a combination of content (known as its matn) and a chain of transmission (its sanad). The chain of transmission includes the original source, the individual who heard it from him, the individual who then heard it from him, and so on. The chain also describes how the transmission occurred between each link. All other things being equal, shorter chains are preferable to longer.
Many people receive an informal introduction to many of the basic concepts of hadith transmission when playing the telephone game. The telephone game is played to teach about the dangers of indirect information and gossip. Players quickly observe, first-hand, how messages become increasingly distorted as they get further and further away from their origin. One of the lessons from this game is that, all other things being equal, we should be more confident in the accuracy of a message conveyed through a smaller chain of intermediaries than we should be in messages conveyed through a chain that is longer.