The not an ASEAN member country is Taiwan (option 4). ASEAN refers to the Association of Southeast Asian Nations, an intergovernmental organization consisting of ten member countries in Southeast Asia.

Option 1: Cambodia is an ASEAN member country. Located in the southern part of the Indochinese Peninsula, it became a member of ASEAN in 1999.

Option 2: Laos is also an ASEAN member country. It is a landlocked country in Southeast Asia and joined ASEAN in 1997.

Option 3: Myanmar, formerly known as Burma, is an ASEAN member country. It is located in the western part of mainland Southeast Asia and became a member of ASEAN in 1997.

Option 4: Taiwan is not an ASEAN member country. Taiwan, also known as the Republic of China, is an island in East Asia. It is not a member of ASEAN as it is not a sovereign state and its membership in international organizations is limited due to political reasons.

To summarize, the correct answer is option 4, Taiwan, as it is not a member of ASEAN.