I've seen alot of apple devices(usually phone's not ipads) get lines like that appear on people's screen's (I've seen pink lines on android as well, but mostly have seen it on apple). Im pretty sure it happens when you drop the device to hard, or when the pixles come in contact with to much water. I'm not sure how to fix it unfortunately, try just taking it to a apple store if it's an apple device. It happened to my old phone before only worse (there were more then one line and there were black spots that grew if you pressed hardly on them) and it just stopped turning on eventually, by the time that had happened i had been given a Android (because that was my preference) and my family didn't notice what happened and when i got the new phone, so i got away with it. They told me to just throw it away because it was a iphone 5 and wasn't getting updated by apple anymore.
