General terms:
* Emergent network: This emphasizes how the network arises from the interactions of its individual components, rather than being planned or designed.
* Self-organizing network: Similar to "emergent network", this term highlights the ability of the network to adapt and reorganize itself without external control.
* Ad hoc network: This term is often used in the context of computer networks, but it can also be applied to social or other types of networks that are formed temporarily and without planning.
Specific terms:
* Flash mob: This term is used to describe a group of people who gather in a public place spontaneously and perform a pre-arranged action, often using social media to coordinate their actions.
* Social movement: This term is used to describe a large group of people who come together to bring about social change. Social movements often emerge spontaneously, although they may be organized over time.
Other possibilities:
* Unstructured network
* Informal network
* Organic network
The best term to use will depend on the specific context and the nature of the network you are describing.