What is a Bus? The Bus is a public communication line, any device can connect to it.
For example, now there are three devices A, B and C connected to the bus, if A wants to communicate with B, that is, A sends information to the bus, and B receives data from the bus. B can communicate with C in the same way.
If there is no Bus and the three devices want to communicate with each other, there will be three wires, one wire between A and B, one wire between B and C, and one wire between A and C. It’s just the interconnection between three devices. What if the number of nodes increases to four, five, or a dozen? It’s really hard to imagine.