General term for the bottom surface of an object, such as a container, device, or structure.
The date of manufacture is printed on the bottom of the box.
底面が滑りにくい素材でできている。
The underside is made of a non-slip material.
In geometry, the face on which a solid figure is thought to rest; often used for prisms, pyramids, etc.
三角柱の底面は三角形である。
The base of a triangular prism is a triangle.