In this context, it refers to how fanout is done. In a bus system, the master (typically) has an address output, a read/write output, and a write data output. These go to all modules in the design. Then the other modules have read data outputs that go to a mux and then to the master.
This is a simplified system. The disadvantages are that there is a large fanout on address/write/cmd lines. This limits the rate the bus can operate at. There are methods that can be used to reduce the impact.
In contrast, AXI doesn't do this. The master talkes to some form of arbiter. The arbiter then talks to each module. In this manner, address/cmd/data only connects to one other module.