Why are Krueger flaps called flaps and not slats? I always thought that flaps are trailing edge high lift devices and slats are leading edge high lift devices. This is also confirmed by the accepted answer for What is the difference between flaps and slats?.

Inspired by this question, I learned that Krueger flaps are actually leading edge devices, despite being named flaps. The definition on SKYbrary is:


  Krueger flaps are high lift devices that are fitted to all or part of the leading edge of the wings of some aircraft types. The aerodynamic effect of Krueger flaps is similar to that of slats; however, they are deployed differently. Krueger flaps are mounted on the bottom surface of the wing and are hinged at their leading edges. Actuators extend the flap down and forwards from the under surface of the wing thus increasing the wing camber which, in turn, increases lift.



(image sources: Wikimedia and SKYbrary)

I understand that the deployment mechanism is different, but the Krueger flaps are still deployed differently than other (trailing edge) flaps:


(image source: SKYbrary)

So why are they called flaps and not Krueger slats instead?
A flap increases airfoil camber, and can be on the leading edge or trailing edge.  The Krueger Flap is a Leading Edge Flap, the actual generic term.  



The Krueger dude developed the LE flap used on some airliners so his name is attached.  

A slot increases stalling AOA, without necessarily increasing camber, as in the fixed slots used on a lot of light aircraft in the 40s to improve aileron control at the stall instead of wing washout, like Stinsons and Globe Swifts, etc.



Combine the slot function of injecting slightly higher velocity air along the top to keep flow attached at higher AOA, and the flap function of increasing wing chord, together on the leading edge, and you get SLAT.   

Or you could say more correctly, Slotted Leading Edge Flap.

Without the slot part though, it's just a flap, as in Krueger Flap.