Stairs are used to create a pedestrian path between different vertical levels by dividing the height between the levels into manageable steps. Very generally, the word ‘stairs’ refers to a staircase, whereas the word ‘step’ refers to the individual steps that make up the staircase. Stairs, particularly in domestic bases, may also include guarding to one, or both sides, in the form of a banister, that is, an assembly of uprights and a handrail.
Stairs can be straight and can include a landing and turn, or can be curved. A continuous series of steps between landings is called a flight. Curved stairs have tapered treads, and can be difficult to use. A helical stair has a void in the middle, whereas a spiral stair has a column in the middle. Under some circumstances, stairs can have alternating treads, that is, the wide part of the tread is on alternating sides on consecutive treads. Stairs can be constructed using a wide variety of materials, including; timber, brick, stone, concrete, metal, glass, and so on.