Keyword Cannibalisation
Keyword cannibalisation occurs when several pages on the same website are optimised for the same keyword and therefore compete against each other in search results instead of against external competitors. Where a site specifies no canonical URL for duplicate or very similar pages, Google states that it determines one itself; as a reason for specifying one explicitly, Google names the consolidation of signals such as inbound links onto a single preferred URL.
In practice
In practice keyword cannibalisation usually happens unintentionally, for example when several blog articles or landing pages on the same topic accumulate over time without a keyword map defining which page owns which search term. The result is above all duplicated maintenance effort for content that overlaps heavily – and a selection decision left to Google instead of being made deliberately. Regular content audits help, as does consolidating overlapping content by merging it, redirecting it or giving each page a clearly different thematic focus.