What does dark yellow urine mean?

Dehydration. Dark yellow urine is a result of dehydration. The kidneys are trying to retain more water. As long as it doesn't burn, all you would need to do is drink more water.
Blood or dehydration. Small amounts of blood, especially if coming from the kidney ann give urine a dark or smokey appearance. Insufficient fluid intake is probably most common cause of dark urine due to concentration. Try drinking 8-10 glasses of water or other low calorie beverages and see if urine clears. Suggest you get urine checked if it remains dark.