Generic Access Profile (GAP)
Generic Access Profile (GAP) is a base profile that defines the basic requirements of a Bluetooth device. All Bluetooth devices are required to implement GAP. It is the basis of all other profiles and it also defines, among other things, how Bluetooth devices discover each other, establish a connection and manage that connection. For example, for Bluetooth Low Energy, GAP defines the Physical Layer, Link Layer, L2CAP, Security Manager, Attribute Protocol and Generic Attribute Profile.
Read more about Bluetooth Core Specifications on the Bluetooth SIG website.