a thick-bladed saw with reinforced back to provide the rigidity necessary in precision cutting
Similar to a miter saw, a backsaw is a handsaw with 12 to 13 points (teeth) to the inch. Often used in a miter box, it produces smooth cuts with or across the grain and is ideal for making delicate cabinetmaking joints. Home Improvement Encyclopedia
Is a crosscut saw with a straight, rectangular blade held rigid by a piece of steel along the top edge and a handle held higher than that of the hand saw. This saw can be used in mitre boxes and for other precision cutting.
A Backsaw is any of several types of hand saws used in woodworking which have a stiffening rib on the edge opposite the cutting edge, allowing for better control and more precise cutting than with other types of saws. Backsaws are normally used for precise work, such as cutting dovetails, mitres, or tenons in cabinetry and joinery. Because the stiffener is thicker than the blade, the backsaws are limited in the depth to which they can cut.
