Okay kiddo, so you know the big building in London where the Prime Minister and some important people work, right? That's called 10 Downing Street. Now, outside the building, there are some people who guard it to make sure nobody bad comes in.
Those guards have a special kind of chair they sit on while they're guarding. The chairs are called 10 Downing Street guard chairs. They're special because they're made of a really strong wood called oak and they have a special design on them that shows that they're part of the guard's uniform.
The guards aren't allowed to move or talk while they're guarding, so they sit on these chairs to rest their legs and make sure they don't get too tired while they're on duty. You might see these chairs if you visit London someday and go to see 10 Downing Street.