What is Buddhism?

When people use the word "Buddhism" often they don't know themselves what they mean.  Zen is not "Buddhism" as most people would use the term.  Certain Zen scholars, historians, and those well versed in comparative religion are more likely to know what they mean when they say "Zen Buddhism."

From: http://www.religionfacts.com/buddhism/fastfacts/differences_theravada_mahayana.htm

	Theravada	Mahayana
Location	Southern (Sri Lanka, Thailand, Burma, Laos, Cambodia, parts of Southeast Asia)	Northern (Tibet, China, Taiwan, Japan, Korea, Mongolia, parts of Southeast Asia )
Schools and Sects	One surviving school (as many as 18 existed at one time)
Buddhist Scriptures	Pali Canon/Tripitaka only	Books of the Theravada Tripitaka plus many other sutras (e.g. Lotus Sutra)
Buddhas	Historical Buddha (Gautama) and past Buddhas only	Gautama Buddha plus Amitabha, Medicine Buddhas, and others
Bodhisattvas	Maitreya only	Maitreya plus Avalokitesvara, Mansjuri, Ksitigarbha and Samanthabadra
Goal of Training	Arhat	Buddhahood via bodhisattva-path
3 Buddha Bodies (Trikaya)	Very limited emphasis; mainly on nirmana-kaya and dharma-kaya	Emphasized, including the samboga-kaya or reward/enjoyment body
Original Language	Pali	Sanskrit
Language of Transmission	Tripitaka is only in Pali. Teaching in Pali supplemented by local language.	Scriptures translated into local language.
Buddha's Disciples	Historical disciples described in Scriptures	Many bodhisattvas that are not historical figures
Mantras and Mudras	Some equivalent in the use of Parittas	Emphasized in Vajrayana; sometimes incorporated in other schools
Bardo (Limbo)	Rejected	Taught by all schools
Non-Buddhist Influences	Mainly pre-Buddhist Indian influences like concepts of karma, sangha, etc.	Heavily influenced by local religious ideas as transmitted to new cultures (China, Japan, Tibet).
Buddha Nature	Not taught	Emphasized, especially in practice-based schools
Rituals	Very few; not emphasized	Many, owing to local cultural influences