The term "barn door" typically refers to a large, sliding door commonly found on barns or other agricultural buildings. However, there are a variety of synonyms that can be used to describe this type of door. These may include words like "sliding door," "barn gate," "barn portal," or "barn entrance." Other possible synonyms might include more specific terms like "horse stall door," "livestock entrance," or "farm gate." Ultimately, the specific synonym chosen will depend on the context and intended meaning of the term, as well as the writer's personal preference and style.