Wiktionary
femtolitre
alt. A unit of volume equal to 10-15 litres n. A unit of volume equal to 10-15 litres
Wikipedia
Femtolitre
The femtolitre (US femtoliter) is the metric unit of volume equal to 10 litres, or one thousand trillionth (European) or one quadrillionth (American) litre. It is abbreviated fL or fl. One femtolitre is the same as one cubic micrometre (μm).