Social Security is a key part of your financial security in retirement, but one problem many have with it is that you can only get your benefits one month at a time. But one little-known secret can get you a one-time lump sum of up to six months of benefits. Is it a smart move for you?

In the following video, Dan Caplinger, The Motley Fool's director of investment planning, explains how the little-known Social Security lump sum provision works. Essentially, if you wait until beyond full retirement age to get your benefits, you can later get up to six months in a single lump sum. But Dan notes that there's a catch: your benefit is calculated as if you'd started taking it six months ago, leaving you with lower monthly benefits. As a result, Dan concludes that those with survivors who'll receive benefits might end up taking a hit over the long run, but single Social Security recipients who get news of a terminal illness might find it useful to maximize their benefits using the strategy.