Mathematical Bold Small Rho

It is a bold Greek rho in the mathematical alphabet. In a formula, its author assigns the value; the glyph does not name one universal quantity. The bold style separates this variable from other math letters.

An early ancestor of this letter is a head picture in alphabetic signs used at Sinai and in Egypt in the early second millennium BCE (before the Common Era). The Phoenicians, an eastern Mediterranean people, called their r-sound letter resh (“head”); Greek speakers later adapted the Phoenician alphabet to write Greek. The earliest surviving Greek alphabetic inscriptions date to the 8th century BCE. In 1463, Benedetto of Florence used rho for an unknown in a book on arithmetic.