Search engines visiting your pages and reading them. It is the step before indexing, and the two are not the same thing.
A page has to be found before it can be read. Search engines find pages by following links and by reading your sitemap, which is why a page linked from nowhere — an orphan page — can sit unvisited indefinitely.
New and small sites get a limited crawl budget. Google will not exhaustively re-read a hundred pages every day on a site with little authority, so the pages you link to most are the ones that get attention.
This comes up most often in Technical SEO & Site Speed. Crawling, indexing, speed, structured data and site architecture — the plumbing that decides whether your pages can compete.
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