The term "pair stair" refers to a set of stairs that has two sections, each with its own set of steps and a landing in between. Synonyms for this term include "double staircase," "twin staircase," "dual staircase," and "bifurcated staircase." These terms all refer to an indoor stairway that splits into two sections, one going up and one going down, with a landing between them. Pair stairs were a common feature in grand homes and mansions during the late 19th and early 20th centuries, and they remain popular today in luxury residences and public buildings.