What is keyword cannibalisation in SEO?
Keyword cannibalisation is when several pages on the same site compete for the same query, so instead of one strong page you have two or three weaker ones splitting whatever authority and relevance you have.
Why it hurts:
Search engines must pick one. They will not rank several of your pages prominently for the same query, so they choose — sometimes the page you did not want, and often inconsistently, with the ranking page changing week to week.
Signals get divided. Links, engagement and internal links that could have concentrated on one page are spread across several. Two pages at position 12 are worth far less than one at position 5.
Internal linking becomes incoherent, because there is no single obvious destination for a topic.
How it happens. Rarely deliberately. Usually through publishing repeatedly on a subject over years, running a blog alongside product or service pages covering the same ground, generating near-identical location or variant pages, or targeting keyword variants that are actually the same query — search engines resolve close synonyms to the same intent even when keyword tools list them separately.
How to detect it: in Search Console, look at a query's performance and check whether the ranking URL fluctuates between pages. Or run a site: search for the query and see how many of your own pages surface.
How to fix it, in rough order of preference:
Consolidate. Merge the pages into one genuinely better page and 301-redirect the others. This usually produces the largest improvement.
Differentiate. If both pages should exist, rewrite them to target genuinely different intents — a guide and a product page can coexist.
Canonicalise where near-duplicates must remain for other reasons.
Adjust internal linking to point consistently at the page you want to rank.
Not all overlap is cannibalisation. Pages covering related subtopics that rank for different queries are a healthy topic cluster.