Most often a straight, lightweight bar containing two or three small liquid filled tubes. The air bubble in the tubes is used to check if vertical and horizontals are level.

Tool used to ensure surfaces are level or plumb by means of a bubble in a tube of liquid fitted to the level.

Level with a fluid filled glass tube that, when held perfectly level, either vertically or horizontally, allows the bubble that is trapped in the tube to be perfectly centered.

A spirit level or bubble level is an instrument designed to indicate whether a surface is level or plumb. Different types of spirit levels are used by carpenters, stone masons, bricklayers, other building trades workers, surveyors, millwrights and other metalworkers.

An engineers spirit level is generally used to level machines, although they may be used to level large workpieces on machines such as planers. Spirit levels are also used in building construction, by carpenters and masons.