In the case of RCC stairs, steps are constructed over a stair slab that has a width up to the full length of the steps. But if the expected loads over stairs are heavy or the span of the stair slab is longer the designer may provide a beam instead of a slab for the economy. Though a beam-slab combination would be economical due to an aesthetic point of view only one beam without a slab is provided with hanging steps that cantilever on both sides of the beam. Such beams are called stringer beams.
In the case of non-RCC stairs where steel, wood, or composite materials are used the stringer beams are frequently used. Sometimes only one stringer beam in the middle is used and sometimes two beams at the sides are used on which steps rest simply supported.