A bus topology is a term from computer science referring to either computer design or network design, not really a question in mathematics.
The "bus" concept refers to having one central line, or 'bus" on which several items are connected. In the original IBM-PC, adapter cards could be dropped into slots on a "bus" data connection, so the PC had a bus topology.
The bus topology concept can also refer to network topologies - how networks are connected together. If all the computers can be connected along a single line, then the network has a bus topology. If the line must go around in a circle, and not terminate, that is a ring topology. If each computer needs it's own cable back to the router, that is a star topology. The visual shape of the wiring gives the term for the type of topology.
This refers to networks with physical wiring. It does not apply to wireless networks.