tongue-twister       
noun [ C ] uk/ˈtʌŋˌtwɪs.tər/ us/ˈtʌŋˌtwɪs.tɚ/
 绕口令
a sentence or phrase that is intended to be difficult to say, especially when repeated quickly and often
  "She sells seashells on the seashore" is a well-known tongue-twister. “She sells seashells on the seashore”是个非常有名的绕口令。