SEO, or Search Engine Optimization, is the collection name for the different methods and techniques that are used to organically rank a webpage or content as high as possible in the search results in the search engines. SEO is a digital marketing process or method.
Content marketing is a methodology where you create content that people want to share and thus earn your visibility in digital channels. Along with your reach comes other valuable drivers such as trust, relationships and anticipation. All of which can be used to drive traffic to places where you can convert people into customers.