Eleanor Mackie is a supposed mysterious, and haunting being, that haunts the ground of Springfield Elementary. Little is known of her early life, as there was only a minimal amount of time in the episode which discusses it, (The Daughter Also Rises.) All that is really known is that she was a student of Springfield Elementary, who drowned in...presumably the girls bathroom of the school.
This is disputed, as the whole story of Eleanor Mackie could of been part of a web of lies created by Bart while, still in his phase of creating myths. The myth states if you go into the girls bathroom and shout, "Eleanor Mackie." Exactly 3 times....well..bad things will happen.