Search Engine Optimization is the process of improving the visibility of a website on organic ("natural" or un-paid) search engine result pages (SERPs), by incorporating search engine friendly elements into a website.
A successful search engine optimization campaign will have, as part of the improvements, carefully select, relevant, keywords which the on-page optimization will be designed to make prominent for search engine algorithms.
Search engine optimization is broken down into two basic areas: on-page, and off-page optimization. On-page optimization refers to website elements which comprise a web page, such as HTML code, textual content, and images. Off-page optimization refers, predominantly, to backlinks (links pointing to the site which is being optimized, from other relevant websites).