Access point networks are the most common topology. As you can see from the diagram there is one central switch, hub or computer, which transmits the network connection. This consists of a central access point, to which all other nodes are connected. The access point is the server and the peripheral nodes are the clients. The access point constitutes a single point of failure.
Contrast that with the decentralization of the ad hoc network which uses a connection between two or more devices without using an access point. The devices communicate directly with each other when they are in range. The ad hoc topology here is a special kind, it is a fully meshed ad hoc topology where every device in range is connected to each other.