Laura Adams gives a perfect definition of marketing in Episode 9: Drive Thy Business of the MBA Working Girl Podcast. "Marketing is the pervasive set of activities that attempt to influence individual or organizational choice."
She also explains why marketing is so appealing to creative thinkers. "There are never any clear cut right or wrong answers in marketing...an unlimited number of combinations of market segments, positioning statements, advertising budgets, prices, channels of distribution ect., exist to consider. There is no secret formula that can be leaned from a textbook that makes the ultimate marketing strategy for a product or service".
This is precisely what makes marketing such an interesting field to study and practice compared to a field like accounting which has very defined rules. In marketing creativity is rewarded, in accounting creativity can lead to jail time.