Self-organization is a form of emergent behaviour where despite no party being in charge, the agents of a system self-organize into groups or clusters that achieve a purpose.
One example might be a group of people deciding to form a book club for social enjoyment, or to better understand something they read by discussing it. Or, ants which hold onto each other to firm a bridge to that the rest of the ants can cross a stream. Company is also an example of this. The founder(s), with a vision and a mission, gather people to help bring this vision into existence.
No one made the members of the system do this, they just naturally perform these actions once integrated into a large enough system.
Connections
Link Explanation: The linked note describes the idea of emergent behaviour, produced by complex adaptive systems. The current note describes one common form of emergent behaviour.