The terms Rare, Medium and Well done are used in the preparation of mainly beef, lamb and veal. They talk about what degree of cooking your meat has, ie how long it is to be fried or grilled and at what temperature. The shorter the cooking time (and the lower the temperature), the bloodier the meat.
The cooking degree affects how the meat looks and tastes. It is of course highly individual how you want your meat, there is no right and wrong here. But some people who believe that that a well-done piece of meat is a ruined piece of meat. But this comes down to preference.
Most people opt for medium when in a restaurant. Then the juiciness is preserved while being properly cooked and not too dry.
The meat is soft and properly red in the middle. Sometimes it can even “bleed” a bit.
The meat is firmer and pink in the middle and a little more fried on the edges.
Gray-brown meat straight through, the meat is very firm.
But there are of course even more roasting degrees!
Here, we only provide inside temperatures for the three most commonly used roasting degrees; rare, medium and well done. But of course in the culinary world, among the pros and geeks, there are of course many more levels of roasting, which speak more precisely about how a piece of meat should be cooked.
This table is shared from Wikipedia and describes a little more about what it might look like: