A spirit level is a tool used to determine whether a surface is horizontal (level) or vertical (plumb). It typically consists of a sealed tube containing a liquid and an air bubble. When the bubble is centered between two marked lines, the surface is considered level. Spirit levels are commonly used in construction, carpentry, and various DIY projects. These tools come in various sizes and types, including torpedo levels, line levels, and digital levels. They are essential for ensuring accuracy in building and installation tasks, helping to create stable and visually appealing structures.