SEO refers to the process of optimizing webpages to rank higher in search engine results. It involves both on-page techniques like optimizing titles, meta descriptions and content, as well as off-page factors like links. Proper site structure, navigation, use of meta tags, optimized images and URLs are important on-page techniques for designers. Page speed, rich snippets and regularly updated content also impact rankings. Understanding SEO techniques is crucial for web designers and developers to build search engine friendly websites for their clients.