Genesis says the Ark had a door made in its side. Genesis 6:16 describes the vessel’s roof and its doorway, placing the door on the side rather than at the top, bottom, or a named end.
The verse is part of a compact description of the Ark’s design. It gives the vessel three levels and also mentions a window or opening near the top, depending on the translation. The text therefore distinguishes the side door from the upper opening.
The passage does not specify the door’s exact dimensions, hinge design, or position along the side. Later artistic reconstructions often add those details, but they are not stated in Genesis. The biblical wording supports the concise answer “its side,” without requiring a particular modern ship term such as stern or bow.