PostEaseThe short answer
A content hub is a central page or resource that organizes and links to a body of related content, typically grouped by topic, making a large archive discoverable and navigable rather than scattered chronologically across a feed. A blog's own category or index pages are a common example.
Why a growing archive needs one
A social media feed and most blog archives default to chronological order, which makes older, still-relevant content harder to find as an archive grows. A hub organized by topic instead of publish date gives a visitor, or a search engine, a much clearer path to relevant content regardless of when it was published.
This is directly related to how a pillar-and-cluster content strategy works
A broad pillar page linking out to a set of narrower, related posts is itself a form of content hub. The pillar functions as the organizing hub, and the cluster posts are the content it makes discoverable. That is the same underlying structure a topic-focused hub page provides more explicitly.