Backsaw

A backsaw has a stiff metal spine folded or fitted along the top edge of its blade, reinforcing an otherwise thin, flexible saw plate against bending or wandering during a cut. That rigidity is exactly what fine joinery work needs -- a dovetail saw and tenon saw are both backsaws, purpose-built (usually differing mainly in blade length and tooth count) for the precise, straight, controlled cuts dovetail and mortise-and-tenon layout lines demand.

The spine does limit cutting depth to the blade's exposed height below it, which is exactly why backsaws are a joinery tool, not a general-purpose one -- deep crosscuts and rip cuts need a saw without that depth restriction.