"水平断面" can be translated into English as "horizontal section" or "horizontal cross-section".
"Horizontal section" is a general term referring to a section or plane that is parallel to the horizon or a horizontal reference plane.
"Horizontal cross-section" specifically emphasizes that it is a cross-sectional view taken horizontally, often used in contexts like engineering, geology, or architecture to describe a view or cut made horizontally through an object or structure.
In most cases, both terms can be used interchangeably, but "horizontal cross-section" might be more precise when you need to emphasize the cross-sectional nature of the view.