Definition of nut straight draw
A nut straight draw is a draw to the maximum straight. If you have 78 on 9-T-x, you have a regular straight draw. But if you have QJ on the same board, you now have a nut straight draw, the maximum straight draw. In this case, not only do you have a nut straight draw, but you also have two cards higher than the board. Even against a player who has top pair, top kicker with AT, you would have a 50% chance of winning the hand from the flop.
Should you play your nut straight draw aggressively?
To use our example above, since we have 50% equity against a hand as strong as top pair top kicker, it will be imperative to play the hand aggressively. By making life difficult for our opponent, we increase the profitability of the hand. Even if he only folds 25% of the time, that's huge! The 25% of the time he folds is our profit. The rest of the time, we win and lose 50% of the time. An aggressive approach is best, especially if you are out of position.