Duplicate Content & Thin Content

Duplicate content is identical or near-identical content appearing on multiple URLs; thin content is a page with too little unique value to justify ranking.

There's no direct "duplicate content penalty" the way many marketers imagine it — Google's more common response is simply picking one version to rank (via canonicalization) and effectively ignoring the rest, which still costs you visibility even without a formal penalty. Thin content (auto-generated pages, near-empty category pages, spun or lightly-reworded text) is treated more harshly and can drag down how the whole site is evaluated, not just the thin pages themselves.