A spirit level, also known as a bubble level, is a tool used to indicate whether a surface is horizontal (level) or vertical (plumb). It is commonly used in construction, carpentry, and other trades to ensure that structures and objects are correctly aligned and positioned.
Spirit levels work by utilizing a sealed glass vial that is partially filled with a liquid, typically alcohol or mineral oil, and a small air bubble. When the spirit level is placed on a surface, the bubble will move to the highest point of the vial. If the surface is level, the bubble will be centered within the vial. If the surface is not level, the bubble will move to one side of the vial, indicating the direction in which the surface is sloping.