Just noticed some serious mis-tagging.
Cross eyed = eyes both toward the nose:
post #253788

Wall eyed = eyes both away from the nose:
post #238920

There are a lot of images tagged as cross eyed that are in fact wall eyed.

Current tags fixed, still leaving this here so people can see the difference for future tags.

Oh, and fyi, Derpy in her typical eye configuration is neither.
Most accurate tag would be lazy_eye, but even that's not entirely accurate because a lazy eye is typically one eye that goes to one side when the other is looking straight forward.
In any case, not cross_eyed.

According to Wikipedia, wall-eye is a euphemism for strabismus, which just means the two eyes don't point together like they should. So Derpy is wall-eyed, yes. As Hammie described lazy-eye, that's actually strabismus/wall-eye.