Crawl Depth is the term given to the depth of a search engine crawler’s search through the webpage hierarchy of a website. The home page of a website is at the top of that hierarchy, with pages that are accessed via the homepage lower down in the hierarchy (at level one) and pages that link from level one pages a further step down (level two).
Crawlers are built to take note of a website’s most important pages, which are usually those that feature higher up the hierarchy. If a website has many dozens or even hundreds of pages, they will require a strong domain authority for the crawl depth to direct search engine bots to inspect many lower-level pages.