As to Wikipedia, "marketing is a social and managerial function associated with the process of researching, developing, promoting, selling, and distributing a product or service."
Oxford dictionary defines it as "an activity or process involving research, promotion, sales, and distribution of a product or service."
My university marketing textbook describes it as "the process of developing, promoting, and distributing products in order to satisfy customers' needs and wants."Marketing involves a lot more than just advertisements and press releases.
It involves creating an entire brand with your product and deciding how: the customer will view it, how they will interact with it pre-purchase, how much they will pay, where and how they will get it, and what they will think about it.
"Marketing" is in the DNA of your product or service, and not something you add to the mix when it comes to making sales.