This specification is used in marketing hype and promotion and is an unreliable figure for determining performance. Ignore it.
Contrast ratio simply put means how bright and how dark an image can be. Human contrast ratio is about 800 and anything beyond that defintely will cause viewer fatigue if not damage. This is based on a dark room at night compared to being outside on a clear sunny day. For most of us just going outside of your house on a sunny day will make your eyes water and squint until your iris closes up to compensate. Of course once you step back in the house...