What the Helpful Content signal actually targets
The HCU signal is a site-wide quality classifier that downweights sites Google judges to be producing content primarily for search engines rather than for people. The official Google guidance lists indicators including: content written to chase keywords rather than answer questions; content that promises an answer the page does not deliver; content that summarizes what others say without adding original insight; content that combines topics that are not coherently related; and content produced at scale without clear human expertise.
Critically, the signal is site-wide. A handful of low-quality pages can downweight your entire site's organic visibility, even on pages that are genuinely high quality. This is why surgical edits to a few pages rarely produce recovery.