The diagonal fraction bar in mathematics. Also called virgule or slash. This symbol was used to replace the horizontal fraction bar, sometimes referred to as a vinculum, due to the typographic difficulty imposed by the horizontal bar which requires three terraces of type.

An early written example of this usage can be found in a 1718 ledger by Thomas Twining. In his article "The Calculations of Functions" from 1845 and published in the Encyclopaedia Metropolitana, De Morgan recommended the use of the solidus.

Also, an ancient Roman gold coin used until the fall of the Byzantine Empire and introduced by Constantine.