Undercooked would be something you shouldn't eat either because it's not safe to do so or it wouldn't taste good (normally this is for chicken, fish, but also vegetables and other things) and is similar to underdone, although if I hear underdone, I don't know if that would mean it is unsafe to eat or just not cooked as long as it should be. Rare is quite bloody but many people like their steaks this way, medium rare is still quite pink, well done is brown with no pink (those are three ways to order steak in a restaurant or at a barbecue). I don't know the difference between 4 and 7, but overcooked is when it is dry and lost some of the flavor from cooking too long. I'm not a culinary expert nor do I eat meat these days, but those are my basic understandings of the terms as a native English speaker. I hope someone else gives you more information!