"Marketing" is a part of business. It means trying to figure out how to sell stuff to customers. It can include how you design products, how you advertise them, and how the company communicates to customers.
"Retail" means stores. So "retail marketing" is advertisements or other promotions that you do in a store. Examples might include signs, people giving out samples, and so on.
The phrase "retail marketing" probably wouldn't make sense to a lot of English speakers unless they work in a large company with dedicated marketing staff.