define ff
FF, Ff, or ff may refer to: â¹ 1 ffâº, a Latin alphabet digraph; it is used in English orthography to represent the same sound as single â¹fâº, a typographic ligature. 2  255 (number) (hexadecimal: FF16), the natural number following 254 and preceding 256.  Femtofarad (fF), 1Ã10â15 farads or units of capacitance.