A simple reference: Laos is always referred to as the country and also the plural of Lao. Lao and Laotian are sometimes interchangeable. Laotian as an adjective refers to characteristics of Laos and its inhabitant; as a noun it refers to the people who are native to Laos, this includes many ethnic groups such as the Lao, Hmong, Mien, etc. Lao on the other hand, usually relates to the people of Lao ethnicity. Lao people reside in both Laos and parts of Northeastern Thailand where they’re called “Isaan” which means “northeast”. Lao can also describe things that are specific to Lao culture and people—Lao language, Lao food, Lao music, etc.