In the Genesis flood narrative, the ark’s only described side opening was a door. Genesis 6:16 instructs Noah to put a door in the side of the ark, and Genesis 7:16 later says that the Lord shut Noah in.
The same construction passage mentions a window or opening near the top, but the door is the sole entrance explicitly identified as being in the side. Genesis does not call it a gate, hatch, or port, and it does not describe multiple side entrances.
The door has a practical role in the story because it provides access for Noah’s family and the animals. It also has literary importance: after the occupants enter, the text says the Lord shuts them in, emphasizing divine protection during the judgment.
Later paintings, models, and film versions add detailed mechanisms and architectural features that are not specified in Genesis. The biblical account remains concise, identifying a side door, an upper opening, three decks, and compartments.