First, we need to define some definitions for the chain of narrations:
- The head of the narration, is the person who is saying the content (المتن) of the Hadith. Mostly it's Prophet Mohamed, but that is not always the case.
- The narrator (الراوي) refers to all of the people in the chain. But usually it points to the person who heard the content of the saying or was there at the event that he narrated.
- Al-Muhaddith (المحدث): I couldn't find an English translation for this, but it refers to the last person of the chain that documented the Hadith e.g. Elbukhari (البخاري) and others. That person documents the content (المتن) and the chain (السند).
The chain usually starts with the end, where المحدث says حدثنا or اخبرنا, which means that he personally met those people in person. However, when المحدث mentions the people in the chain he uses the word عن, which means that the person the محدث actually met heard this from that person after that word and the chain goes on. But nowadays people use the word عن directly, which essentially gives it the same meaning as the previous words.
But fourth word is in passive form which means that there is a person in the chain unknown unless that unknown person was mentioned like: سمعت من فلان. And the chain goes on. In Bukhari, you could find different Hadith that have multiple paths of narrations leading to the prophet.