Keyword cannibalization happens when two or more pages on the same site target the same keyword and search intent, forcing Google to choose between them. Instead of one strong page you end up with several weaker ones splitting clicks, links, and relevance signals — and rankings wobble.
The classic symptom is two URLs from your domain swapping positions for the same query week to week, neither able to hold the top spot. You can confirm it with a site:yourdomain.com "target keyword" search, or in Search Console's Performance report: filter to a query, open the Pages tab, and if several URLs each pick up impressions for it, they're competing.
A software blog had three posts — "best CRM tools," "top CRM software," and "CRM tool comparison" — all chasing the same buyers. None cracked the top 10. Merging them into one definitive guide and 301-redirecting the two weaker URLs into it consolidated the backlinks and pushed the surviving page to position 5.
Options for untangling cannibalization:
Preventing overlap starts with disciplined keyword mapping in on-page SEO, and a content gap analysis helps you find genuinely new topics instead of rehashing ones you already cover.