Class 1 EFB: portable commercial-off-the-shelf computer systems like laptops, tablet PCs or personal digital assistants. They are neither attached to nor integrated with the aircraft. Typically use only Type A and B, uncertificated software applications. May not be used during take-off, approach or landing.

Class 2 EFB: like Class 1 devices, but have a mounting station in the cockpit and possibly some connectivity to non-essential aircraft systems.

Class 3 EFB: built into the flightdeck, electronically integrated, can host Types A, B, and C software. Requires certification. Subject to software development requirements, usable in all flight phases.

Source: Flight International