A teeter-totter is the playground toy that is a long board balanced in the middle, with a child sitting on each end: one goes up as the other goes down. This is the American word. In Britain, Australia, and in most of the English textbooks used in Taiwan, the same thing is called a 'seesaw' — and 'seesaw' is by far the commoner word worldwide, so learn that one first and keep teeter-totter as the American variant you will meet in American children's books and films. Even inside the United States it is regional: it is strongest in the Midwest and the northern states, while plenty of Americans elsewhere say seesaw too. Write it with the hyphen. There is also a verb 'to teeter-totter', meaning to ride one or to rock up and down, but it is not common; the plain verb 'teeter' is the useful one — 'to teeter' means to stand or move unsteadily, as if about to fall ('She teetered on her high heels'), and it is often used figuratively: 'The company is teetering on the edge of bankruptcy.'

蹺蹺板。台灣課本通常教 seesaw，那是英式與國際通用說法；teeter-totter 是美國（尤其中西部）的講法，兩個是同一個東西。