Semiorders are binary relations that are complete, Ferrers, and semitransitive. In particu- lar, they display a transitive asymmetric part (strict preference), and a usually intransitive symmetric part (indifference). Semiorders are among the most studied categories of binary relations in preference modeling. This is due to the vast range of economic scenarios which can modelled by appealing to the notion of ‘just noticeable difference’. We give a univer- sal characterization of semiorders, which uses the notions of a Z-product and a Z-line.