What does it mean when your pee is really really yellow?

Dehydration. Usually means dehydration and not drinking enough water. Institute of medicine determined that an adequate intake for men is roughly 3 liters (about 13 cups) of total beverages a day. The ai for women is 2.2 liters (about 9 cups) of total beverages a day.
Dark urine. Commonly that is the result of food intake that has color or dehydration. However, if the color does not become normal soon, then see your doctor. One test is to drink several glasses of water and see if the urine becomes nearly clear.