Department store Macy's Inc. (NYSE:M) saw its revenue miss Wall Street forecasts in the third quarter, causing the retailer to lower its earnings outlook for 2014. Meanwhile, Macy's same-store sales, a key metric in the retail sector, dropped 1.4 percent in the previous quarter, concerning investors. Same-store sales compares the sales of stores that have been open for at least one year and allow investors to determine what portion of new sales has come from sales growth and what portion can be attributed to the opening of new stores.