steps (staircase units) <p>Staircase units that consist of one tread and one riser, or any similar element providing a horizontal surface on which to support the foot of a person descending or ascending.</p> <p>Source: Art and Architecture Thesaurus<br /><a href="http://vocab.getty.edu/page/aat/300003312">http://vocab.getty.edu/page/aat/300003312</a> </p>