What is the definition of Bluetooth peripheral device?
Master (or "central") devices
Scan for other devices. Usually, the master is the smartphone/tablet/PC.

Slave (or "peripheral") devices
Advertise and wait for connections. Usually, the slave is the BLE module.

Client devices
Access remote resources over a BLE link using the GATT protocol. Usually, the master is also the client.

Server devices
Have a local database and access control methods, and provide resources to the remote client. Usually, the slave is also the server.