In SEO, "crawling" refers to the process where search engine bots, also known as web crawlers or spiders, systematically browse and index web pages on the internet. These bots visit websites and follow links to gather information about the content, structure, and other elements of each page, which is then stored in the search engine's database. Crawling is a fundamental step in search engine optimization as it ensures that web pages are discovered and evaluated for their relevance and quality in search engine rankings.