A carpenter's level, also known as a spirit level, is a tool used to determine if a surface is horizontal (level) or vertical (plumb). It typically consists of a long, straight bar with one or more vials filled with liquid and an air bubble. When the bubble is centered between the marked lines in the vial, the surface is considered level. Carpenter's levels come in various lengths and materials, including wood, aluminum, and plastic. They are essential for construction and woodworking projects, ensuring that structures like walls, shelves, and cabinets are properly aligned. Accurate leveling is crucial for both aesthetics and functionality in building.