Upvote:2
The three major sects would be Hīnayāna - the small vehicle/path; Mahāyāna - the great vehicle/path and Vajrayāna - the diamond vehicle/path. For differences compare this thread: What are the main differences between the Theravada, Mahayana and Vajrayana branches of Buddhism?
Upvote:9
Mahayana is not a sect at all; it is a vehicle.
Major traditions in Buddhism are usually country or region related. We can distinguish three major branches of Buddhism in the World by what they keep as canon.
Some countries mix several aforementioned branches.