Dictionary.com
definitions

SEO

search-engine optimization: the methods used to boost the ranking or frequency of a website in results returned by a search engine, in an effort to maximize user traffic to the site: The first step in SEO is to generate keywords that are relevant to your site's content.
See also SEM(def 2).
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for search engine optimization

search engine optimization

search engine optimisation

noun

computing the process of adjusting the content, structure, etc, of a website so that it will be displayed prominently by a search engine

SEO

abbreviation for

computing search engine optimization
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012