Father Steve: How nice to see your post. Where have you been all this time?

To me a fret saw is a modified backsaw used for cutting the slots on the fingerboard of a stringed musical instrument such as a guitar. An adjustable depth stop is used to keep the cuts uniform and in fitting with the tang of the fret.

See

http://www.stewmac.com/cgi-bin/hazel.cgi?action=SERVE&ITEM=catalog/sku.html&sku=5320