It can be and often is used with the other strategies above.
Dollar-cost averaging (DCA) is when you make regular investments over time, as when you set aside part of your paycheck for your 401(k). It can be and often is used with the other strategies above. However, the point of this is discipline: even if the market is going down or you're most worried about investing, you still put away a set amount periodically. This means you benefit when stocks are low and you can buy more with the same amount of funds.