Definition
Content freshness is how recently a page was published or substantively updated, and whether that date is stated in a form a machine can read. Retrieval systems use recency signals when a question implies a current answer.
Why it matters
Undated or wrongly dated pages lose to dated competitors on exactly the questions where recency matters most, such as pricing, comparisons and anything with a year in it.
How to measure it
Check that published and modified dates exist in structured data, that they are visible on the page, and that they reflect real edits. A modified date bumped by a build is a lie a crawler can catch.