The bow saw falls into a generic class of saws called "frame saws".  These can be tiny fret saws for marquetry work or huge frame saws for cutting logs or resawing boards.  The "Bow Saw" is the middle of the road sized saw with a blade generally 18-24" in length.  They can be used just like and 26" western rip or crosscut saw but these saws are shop made using very little steel.  Often referred to a Continental Saw because the cabinetmakers in Europe who didn't have access to the industrial resources of England and wide saw blade steel.  Instead they used skinny strips of spring steel and wood in their own shops to build a wide range of saws.

This lesson walks through the entire build step by step.  I build an 18" long saw in the video but I show how to size your own saw proportionally as well as how to make the saw blade from scratch.  The key comes from the proportions and you could even make multiple blades to fit a single frame and have all kinds of custom sawing solutions at your finger tips for a tiny fraction of the cost it would take to buy a bunch of English pattern (or even Japanese) saws.