An open field or vacant lot with grass or bare ground; a plain often used as a playground or picnic spot.
子どもたちは原っぱでサッカーをして遊んでいた。
The children were playing soccer in the field.
週末は公園の原っぱでピクニックをする予定だ。
We're planning to have a picnic on the park's open field this weekend.
この原っぱは春になると花が一面に咲く。
This field becomes covered in flowers in spring.