Oyabun (i heard this word in one piece anime)

when i first heard oyabun, i think that oyabun is like word okaasan ora obaasan in japan. but i'm not sure with my conclusion. i began to search in my japan dictionary. i found that oyabun is words to define the supervisor or crime boss.

i search in wikipedia as online encyclopedia , it said that oyabun is like acriem boss or something like that. i'm not sure if im right. if you have another idea what is oyabun, please inform me.

thank you..