A breathing hole is a small opening or gap in a surface or material that allows air to flow in and out. There are several other synonyms for breathing hole, such as air hole, ventilation hole, air vent, and airflow passage. The term breathing hole is commonly used in the context of underwater diving, where divers need to have access to air while being submerged. However, it can also refer to any opening in a structure or material that allows for proper ventilation and air circulation. Regardless of the variation of words used, they all refer to openings that allow for the movement of air.