The term "Thailand tea" or "Thai tea" can have different meanings and is not widely used in a consistent way in the U.S.
Thai iced tea is a particular drink made out of blending iced tea with sugar, evaporated milk or coconut milk, and often spices. This drink is widely served in the U.S., especially in Thai restaurants. It is often, but not necessarily, made with tea grown in Thailand.
Strictly speaking, Thailand tea or Thai tea just refers to tea produced in Thailand. Tea from Thailand is not as well-known as tea from China or Japan, but Thailand does produce tea, including green, black, white, and oolong teas.