Terms like "stairs," "staircase" and "stairwell" invoke some of the same images, but these terms do not mean precisely the same thing. To complicate matters further, all staircases refer to stairs, but not all stairs refer to a staircase. By understanding how the architecture works, you can easily distinguish between stairs and staircases.
A stair is any step included as part of a series leading to a different floor or level. When only step is present, the word "stair" is typically not used, since the word "stair" connotes a series of steps leading to a higher or lower elevation. Stairs may consist of a variety of materials, including wood, carpeted wood, steel or concrete, and may exist independently or as part of a staircase.
A staircase is a structure unto itself that holds a series of stairs. The stairs in a staircase usually consist of different parts, independently constructed for the overall support of each step. These parts include stringers, which run along the sides of each stair for support; risers, which make up the vertical part of each step; and treads, which make up the horizontal section where you place your feet.
In addition to having stairs consisting of multiple materials, a staircase may also begin with a firm starter step, or swell step. Additionally, a staircase will typically contain contain a balustrade, which contains a series of vertical balusters, or posts, to keep you from falling off the side, thick starter posts and hand rails. These parts all work together to construct a solitary, firm staircase.
While a staircase contains a number of stairs, the term refers to a single uniform piece of architecture, including the stairs themselves and all of the parts that hold them together. If a series of stairs exist independently, like a set of concrete steps molded on the slope of a hill, it may not be referred to as a staircase, but simply as a series of stairs or steps.