Overnight positions are trading positions that are not closed by the end of the traders trading day. They're then held open for trading to proceed the following day. Overnight positions expose the traders to risk from adverse movements happening when trading closes for the night.
Scalping and swing trading are very common ways to make your profits while trading. Each has advantages over the other and they have their disadvantages, too. No matter the type of trader you are, the other trading style still must be recognized as it can move markets in its own way and can catch movements that the other side would not catch. So, whether you trade like Shawn Lucas and scalp or if you do a longer term swing trade approach, knowing the difference and what they can add to your trading is important if you're adapting to the new strategy.