The name of a
sign frequently used by
British signers, although I have been unable to ascertain whether it is '
officially' part of
British Sign Language at this time. It is an
expression of
enthusiastic approval, roughly equivalent to "
Great!" or "
Cool" in
spoken English.
To make the sign, hold one hand open, palm up, fingers pointing away from you, and with the other hand form a fist with the thumb extended (ie., the classic 'thumb up' sign). Now strike the open palm with the heel of the fisted hand, and quickly raise the fist, thumb still aloft, until it's roughly shoulder-height. It should look almost as if the fist has bounced off of the palm. As with all signs, your facial expression should also mirror the sentiment expressed by the sign.
Of course, in order to explain here how to make the sign, I've had to write it as if it actually consists of several isolated movements. In practice though it is all done in one smooth move.
'Fi' probably gets its name from the fact that an exhalation of breath often accompanies the strike of fist on palm, making a 'Fff!' sound or similar. Even signers with no sense of hearing tend to make this exhalation. If you want to know why, I suggest you try it for yourself: it just feels right.