Fiddleback is really "curly grain in wood". There are different degrees of curl. The term fiddleback comes from the very tight amount of curl that has been traditionally used on fiddles (violins, cellos etc.)
I have heard that "if the curl ihas four or five to the inch then it is referred to as fiddleback curl" If it has fewer than rhar it is just referred to as curl or curly wood.
Noone seems to know why curl or bird's eye happens in wood for sure.
I use a lot of "curly" woods and a tung oil will bring out the curl better then most products. You may use other finishes over that if it has been allowed to cure porperly. Many times I will just use a good wax, IE: Black Bison, over the oil finish. I do on occasion use a water base finish over the oil.
I hope that will help you with Fiddleback.
I often describe fiddleback grain as like a tight wavy hair perm.
When you cut through this grain , you are looking at alternating end grain and then along the grain. If you move while looking , you'll notice that the wood appears to shimmer as if alive. Working highly fiddlebacked timber is not easy because of the severe curl but the results are well worth the effort. This fall front desk is in fiddleback maple silkwood.