Changing the Guard

Từ điển Oxford Advanced Learner 8th

Changing the Guard [Changing the Guard] BrE NAmE
a traditional and formal ceremony that takes place in London, England, when one set of soldiers guarding a royal building replaces another on duty. It takes place every day in summer, and every two days in winter outside ↑Buckingham Palace and outside the ↑Horse Guards building on ↑Whitehall, and is very popular with tourists.