I have read books that foreshadowed things that only happened six books ahead.

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Writers that don't follow the rule of Checkhov's Gun (never show something in a scene that won't be used later) can accidentally foreshadow something you don't intend by placing something in a scene that doesn't actually go anywhere.

and whodunnit mystery writers deliberately foreshadow red-herrings to keep us guessing  

Foreshadow, the art of skillfully leaving clues without ruining the story for the readers.  If you do it correctly, when the readers discover what you've been foreshadowing, they will smack themselves in the forehead and say, "Damn, I remember he said or showed us that earlier, but I never put it all together until now!"