I found in my textbook this sentence:<br/><br/><i>Not all advertising is about selling products and services for a profit.</i><br/><br/>Is "profit" not an uncountable noun? Why is "a" modifying it here? It really confuses me. <br/><br/><a class='_ac _lb' lightbox='http://www.EnglishForward.com/English/images/misc/progress.gif '><img class='_ac _di img-fluid' style='height:inherit; background: inherit;' data-delaysrc='http://www.EnglishForward.com/English/images/misc/progress.gif' src='http://www.EnglishForward.com/English/images/misc/progress.gif' /></a>