Glossary /Foundations
Indexing
Storing a crawled page in the engine’s searchable database, the step between being fetched and being eligible to rank.
Indexing is what happens after a fetch succeeds. The engine renders the page, works out what it is about, decides whether it is worth storing, and files it. Being crawled does not guarantee being indexed — engines routinely fetch a page, evaluate it, and decline.
The most common reason for a declined page is that the engine already has the same thing. Near-duplicate pages, thin pages generated from a template, paginated archives and parameter variations all get dropped as redundant. "Crawled — currently not indexed" is usually the engine saying this page adds nothing, not that something is broken.
Indexing is also reversible. Pages fall out of the index when they stop being fetched successfully, when a canonical points elsewhere, or when the engine reassesses them as low value. Treating index coverage as a number to monitor rather than a milestone to hit is the correct posture.