It has several names. Most call it a stencil knife. Printers and art people use them.
A similar knife is called a bleeding knife, but the blade shape is slightly different. They are used by vets to cut animals for bleeding and sub-dermal parasite removal.
Another similar knife is a frog knife, used by farriers for cleaning hooves, or by horsemen for removing stones and splinters from a hoof.
Blade could use a little TLC.