Keyword cannibalisation happens when two or more pages on the same website target the same keyword or very similar keywords. Instead of working together, these pages compete against each other in search results. This splits traffic between them, weakens their individual authority, and makes it harder for any single page to rank well.
Search engines may struggle to decide which page is most relevant, so they often show different pages at different times, or none of them performs as strongly as they could. You can fix keyword cannibalisation by merging similar content, using proper internal linking, setting clear canonical tags, or adjusting the focus of each page to target distinct keywords.