What does the integration of Bluetooth module master and slave mean?

Generally speaking, Bluetooth communication refers to the communication between two devices, just like making a phone call, one person communicates with a mobile phone;

Host refers to the party that can search for others and actively establish a connection. For example, I took the initiative to call the other party.

Slaves can't take the initiative to establish a connection, but wait for others to connect themselves and keep listening (waiting for others to call);

The current state of a module can only be in one of them, either in the master module or in the slave module.

Master-slave integration means that you can switch between master mode and slave mode, usually by pressing a button, and you can choose to work in master mode or slave mode.