Is this a dead pixel or stuck pixel? I've tried the apps and I've tried to apply pressure this hasn't worked at all, so I phoned Apple they tried helping over the phone. That didn't work. They said my warranty covers it but I want to know what it is? They said it sounds like a dead or stuck pixel.

MacBook Pro (Retina, 13-inch, Mid 2014)
It could be dead pixels or it could be the driver 'chips' or a dead 'mux'. The hardware that control what pixels are turned on. Note the color, It looks to me like a group of pixels are 'turned on' when they shouldn't be. It is hard to tell just by looking at a picture. It could be anything in the graphics display hardware. Just let Apple replace it, no one troubleshoots to component level these days.