De-indexing means removing a page from a search engine’s results. It can make a page harder to find through ordinary searches, but it does not necessarily restrict access: anyone with a working URL may still be able to open it. De-indexing is therefore a visibility measure, not an access-control mechanism.
In cyber security, this distinction matters when sensitive material is shared through links. A page omitted from search results may still be discoverable through other sources, such as link lists or historical DNS data, and may remain accessible to anyone who obtains its address. Defenses should rely on authentication, authorization, and revocable permissions—not obscurity alone. De-indexing can reduce exposure, but it cannot replace those protections or guarantee that copies and caches are removed.