Schools of Buddhism

In the sense of “traditions” or “lineages”. It is difficult to do justice to each path of Buddhism in a summary, but one that might be useful is:

Theravada, or “Pali tradition”, is based upon the Pali Canon as its sole scriptual source. It’s no b.s., cut-to-the-chase. Anapanasati and vipassana are key.
Mahayana, or “Sanskrit tradition”, covers numerous schools. Mahayana has Sanskrit scriptural sources outside of the Pali Canon.
Well-known branches of Mahayana are Tibetan Buddhism and Zen Buddhism.
Tibetan Buddhism is heavy in culture and rituals, with colorful iconography. Its meditation practices use more visualisation and imagery. It has many sub-schools of its own.
Zen is another form that goes in the other direction — it is very straightforward and emphasizes zazen.

As it is human nature to find many paths to the same truth, there are many sub-schools as well. Going deeply into each one seems to find one right back at the same central concepts.

Good discussions of the different schools of Buddhism:
http://newbuddhist.com/discussion/4346
http://newbuddhist.com/discussion/4605/theravada-mahayana-buddhism-big-difference