In it’s original and purest form SEO refers to the practice of tailoring the content of web pages to improve their ranking in Search Engine Results Pages (SERPs). Today that includes on-page optimization (use of keywords, etc.) and off page optimization (link building, etc.).
However the term has grown to encompass all manner of online marketing including many that are not directly related to search engines. A few examples include:
- ad campaign management
- reputation management
- social media marketing
- conversion optimization