The consistency of meconium may be characterized as thick, thin, or moderate. Most doctors feel thick meconium poses more of a potential problem although thinner meconium has been known to cause difficulties as well. Terminal meconium describes the timing of when it was passed. Theoretically, the longer meconium is present in the amniotic fluid, the greater the risk of aspirating it. Once the head is delivered, the only meconium that could possibly be aspirated is that which is sitting in the mouth.
Terminal meconium is that which passes once the head is delivered.
Therefore, if no meconium passed while still inside mom, terminal meconium is of no consequence. It is possible that the passing of the meconium was due to the wrapped cord, however, it may also just be that your baby decided to pass meconium at that time. In answer to your second question, a baby, like most humans, can only go several minutes without oxygen and not suffer some brain damage. However, I would caution you on interpreting your baby's situation. A nuchal cord does not necessarily mean oxygen is cut off.