SYS/DEF
Cannibalisation
Two URLs on your site fighting the same intent — Google often picks one, and not always the right one.
Definition
SEO cannibalisation is several pages targeting the same search intent with comparable relevance. The engine oscillates, dilutes link signals, and sometimes serves the product page, sometimes a dated blog post. It is not “too much content”: it is too much content for the same query.
You diagnose it by query, not by page count. Two URLs sharing impressions for one intent cluster, swapping positions 8 and 12, is the symptom.
When it matters
Before you write yet another “guide”, and after an IA refactor. A well-held semantic cocoon avoids cannibalisation by giving each URL a role (pillar, support, transactional).
It also matters in SEA: a landing that duplicates an organic URL already at #1 can raise Quality Score… or cannibalise the organic click you were getting for free.
Pitfalls
Merging two pages that do not share intent (informational vs transactional) because they share a word. Shipping a 301 without updating internal links. Confusing cannibalisation with e-commerce pagination — different problem, and a bad canonical makes both worse.
Related terms
Related tool
Put a number on the organic traffic of a URL once it is no longer competing with its sibling: Open value of SEO traffic.