An audit entry has to say not just who acted and how, but on what. The entityType answers the "what kind of thing" half of that — it holds a label like "Artifact", "Project", "Feature", or "ExcavationUnit" identifying the type of record involved. Combined with entityId, which pins down the specific record, it lets Relic reconstruct the full history of any single object. It is also indexed together with entityId, so pulling up "everything that ever happened to this artifact" is a fast, direct query rather than a scan of the whole log.
Technical section
Data model, API, and internals — visible to developers.