A: A Bluetooth protocol stack is a set of layered programs. Each layer in a protocol stack talks to the layer above it and the layer below it. Below a Bluetooth protocol stack is the baseband, which
consists of radio hardware and the software that directly controls the radio; above it are Bluetooth profiles. A profile is a set of instructions for using the protocol stack in a certain way. There are different profiles for different types of devices and
different purposes. For example, a cell phone might implement the Headset Profile, while a fax machine might implement the Fax Profile. Profiles can be thought of as purpose-specific constraints put on the use of the underlying multi-purpose protocols, where
such constraints help to ensure interoperability between devices using the same profile.
From: http://www.oi-us.com/service/faq_pre_stack_details.htm
