"Marketing" in the pure academic sense is the entire collection of activities that create value, give that value to customers, and extract some of that value in return. By this definition, sales is a subset of marketing.
This definition always caused me to roll my eyes when I heard it from profs, "Everything from R&D to operations falls under marketing" but it actually proves valuable; limiting your thinking about marketing to promotion and sales means you leave a lot of opportunities unexamined.
It is a particularly broad definition. One could argue that 'anything in business can fall under marketing in some way'.
A personal definition I like to use is 'marketing is any activity designed to increase the top-line sales revenue number'. If you research and launch a new product, that's marketing. If you cold call, that's marketing. If you write inventory control software, that's not marketing. If the software reduces delivery time, that's marketing (since you could argue that improved delivery time translates to increased customer satisfaction, and ultimately increased sales).
This definition always caused me to roll my eyes when I heard it from profs, "Everything from R&D to operations falls under marketing" but it actually proves valuable; limiting your thinking about marketing to promotion and sales means you leave a lot of opportunities unexamined.