A hub contains a single collision domain and a single broadcast domain, regardless of the number of ports on the hub.

A broadcast domain is created any time you connect several clients together via a network connectivity device, such as a hub or switch or bridge. They would all be in the same broadcast domain for every client connected to them.

Since a router does not forward broadcast messages, it creates different broadcast domains.

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A collision domain consists of all the clients that could possibly cause a collision amongst themselves by sending a packet at the same time. Devices such as hubs create a single collision domain which means that everyone connected to the hub has the capability of causing a collision (which is a problem).

A broadcast domain consists of all the clients that can receive the same broadcast packet. Unlike a collision domain this is not a problem. Think of it as those systems that are capable of receiving the broadcast message.