A spirit level is a tool used to determine whether a surface is horizontal (level) or vertical (plumb). It typically consists of a sealed glass tube filled with liquid, usually alcohol, and an air bubble. When the bubble is centered between two marked lines, the surface is considered level. Spirit levels come in various sizes and types, including carpenter's levels and torpedo levels. They are commonly used in construction, woodworking, and home improvement projects to ensure accuracy in alignment. Proper use of a spirit level helps achieve professional results in building and installation tasks.