The schoolyard or playground — the outdoor area on school grounds used for sports and play.
明日は校庭で運動会が開かれる。
The sports day will be held on the schoolyard tomorrow.
放課後、子どもたちが校庭で遊んでいる。
After school, children are playing in the schoolyard.
雨で校庭がぬかるんでいるから外では遊べない。
The schoolyard is muddy from the rain, so they can't play outside.