I'm new to archery and bought a book. However, the author is often using the term "bow shelf" and I can't really imagine what this might be.
So, what is a "bow shelf"?
The answer is really simple. It's the little "cut out" just above the grip. This edge where you can "lay down" your arrow while you shoot. A picture might help:
Note: An "arrow rest" is something different!
Some notes on the different designs which may occur:
There are 3 basic types of shelf designs; flat, radiused and ridged. The diagrams below picture these 3 variations.
The radiused shelf is the most common on both longbows and recurves. As illustrated in the picture, the radius reduces the amount of arrow-to-bow contact.
The flat shelf is also relatively common, especially on some older styled recurves. When a bow has this style of shelf it is necessary to use an elevated rest to get the fletching clearance necessary for good arrow flight. One trick that has been used in this situation is to place a thin narrow strip of leather under a rug rest and continue it up the sightwindow under the strike plate. This will allow more clearance and therefore help with flight.
The ridged shape, I believe, is the design that offers the best clearance, since the arrow-to-bow contact is at its absolute minimum.