About.com says a recession is when there's a decline in the Gross Domestic Product (GDP) for two or more consecutive quarters.  A depression is when the GDP declines by more than 10 percent. 

Both definitions are up for debate, but one rule of thumb is that people can't decide when we're in a recession or not, but nobody questions when it's a depression.  In other words, if you're eating meals at food kitchens, we're probably in a depression.  If not, it's probably a recession.