Fajr: Morning prayer, which is offered after dawn and before sunrise. Dawn.
Faraq: Another word that is used as a substitute for talaq which means separation.
Fard (pi. Faraaidh): Obligatory. Compulsory.
Fardu Ayn: A compulsion on every Muslim male and female
Fasakh: When a marriage contract is annulled from the side of wife.
Fasid: Wrong (null and void).
Fay: Spoils of war.
Fee Sabeelil Laah: In the way of Allah.
Fijar: Sacrilegious war. This battle took place among the Arabs before Islam. It was given this name because it violated the sacredness of the Haram and the sacred months. These months were regarded as sacred and respected among the Arabs even before Islam.
Firqatu Fashkin: Dissolution by annulment.
Firqatu Talaqin: Dissolution by divorce.
Copied from 'THE ISLAMIC SCHOLAR'