Click depth
Click depth is how many clicks it takes to reach a page from your home page. Pages buried deep are harder for people and bots to find.
Click depth counts the clicks a visitor needs to reach a page, starting from your home page. A page linked from your main menu has a click depth of 1. A blog post you can only reach through the blog, then page six of the archive, then the post itself, is much deeper.
Crawlers find pages mostly by following links, the same way people do. The deeper a page sits, the fewer paths lead to it, and the less often a bot is likely to come across it. If your best answer to a common question is buried, the platforms may never read it.
Why links say what matters
How your pages link together also tells crawlers what you think is important. A page linked from the home page and from a dozen related pages looks central. A page with one link from an old archive looks like an afterthought, however good it is.
For example, Harrow & Pine writes a thorough guide to choosing coffee for an office. It sits five clicks deep in the blog archive, and only one other page links to it. Linking it from the main menu and from the office products page brings it to a depth of 1, and gives bots three ways in where there was one.
How to keep pages shallow
Keep the pages you most want found within two or three clicks of the home page. Link related pages to each other, with link text that says what the page is about. Group pages on one subject under a pillar page that links to all of them.
A sitemap helps bots find pages, but it doesn't show how pages relate. Links still do that work.
In AnswerOrbit
The Pages tab in Website lists your pages with their bot visits, once you've connected your server logs. If a page you care about gets few bot visits, check how many clicks it takes to reach it.