There are two meanings: To hope that something happens. You can't affect (/influence) it, but the gesture (to cross your fingers) helps to rise your chances. To reverse (/turn back) a promise the moment you give it. You don't intend (/want) to keep it. Both are superstition. They don't work. Believe me... In your case it sounds like an invitation: Keep your fingers crossed! Someone wants you to wish him/her luck. That something might become true.

It means to hope for luck

This is an expression AND an actual gesture. If the gesture is made, the one meaning "good luck" is made in front of the body, with the palms of the hands facing out or in: http://haikugirl.files.wordpress.com/2007/11/450election_cantwell_fingers.jpg If it is done meaning the the person is lying (usually by children, but used in print media to show dishonesty in anyone), it is done behind the back: http://www.consumermediapublishing.com/images/GuyFingersCrossed_L.jpg This is NOT the gesture or phrase used when praying. For praying, the fingers are "interlaced". We call this "folding your hands": http://www.fcofb.org/prayer_hands_folded.jpg This is called "folded hands" even if it is not done in prayer: http://www.productbeautiful.com/images/hands_folded.jpg

it is an idiomatic expression that could mean 'hope for a good outcome or result' or 'wishing for luck' "I'm one among the contestant in our class spelling bee. Keep your fingers crossed" or it simply means, "WISH ME LUCK!" I don't know how true this is but I don't go on trying his one! :)

The oral phrase "keep your fingers crossed" is a little of both of the above responses. It is used as an oral expression of hope when you will enter a situation, you hope/wish for the best outcome. The other way it is used is to hope a bad situation will become a good one. :-) (crossing your fingers is different from the oral expression here, but it's an interesting thing as well) ^_^ Enjoy!~