Bluetooth LE

Also known as BLE. Not to be confused with Bluetooth, which is completely different except for where it's the same.

GATT

The Generic Attribute Profile is the core BLE API. A server implements services, which are collections of one or more characteristics, and may have zero or more secondary services. A characteristic has a value, and optional descriptors. All three of these objects have UUIDs. Some UUIDs are assigned, and refer to standard objects. Others are vendor-defined. The UUIDs of a server's services, their characteristics, and their descriptors can be enumerated, but the client must give meaning to them (they are not self-describing).