Indochina can be considered as the mainland of Southeast Asia, and there are 6 countries in Indochina including Cambodia, Laos, Malaysia, Myanmar, Thailand and Vietnam.
Modern definitions of South Asia are consistent in including Afghanistan, India, Pakistan, Bangladesh, Sri Lanka, Nepal, Bhutan and Maldives as the constituent countries.
Southeast Asia is a subregion of Asia, consisting of the regions that are geographically south of China, east of the Indian subcontinent and north-west of Australia.