undocumented

In a legal or social context, "undocumented" is a neutral or empathetic term used to describe people living in a country without valid visas or residency permits. It is generally preferred over more pejorative or harsh terms like "illegal alien," which can be seen as dehumanizing. The term focuses on the status of the paperwork rather than the character of the person.

In technical or professional contexts, such as software engineering or corporate auditing, "undocumented" refers to features, bugs, or procedures that exist in practice but are not listed in the official manual or documentation. This often implies a "hidden" or "secret" quality, where knowledge is passed down informally (tribal knowledge) rather than through official channels.

When used in historical or academic contexts, it describes events or populations that left no written trace, emphasizing a gap in the archival record. This differs from "unknown," as "undocumented" specifically highlights the absence of a written record rather than a total lack of knowledge.