TL;DR
Keyword cannibalization represents content placed on multiple pages or articles across the same site using the same keywords or very similar ones in order to rank higher in search engines. This often ends up creating pages that compete with each other.
What is keyword cannibalization?
It sounds absolutely terrifying, but the concept of keyword cannibalization is rather old, and a very common problem in the SEO structures of many websites. It identifies the problem of having several pages competing for the same (or extremely similar) keywords/keyword clusters.
This often unnoticed problem impacts the SEO potential of your pages in a bad way. If more than one page has the same keyword target as another page on your website, it generates “confusion” in the search engine. This results in an unnecessary struggle to decide which page to rank for what term.
There is a fairly common misconception that the more pages you have targeting a keyword on your website, the higher you will rank for that keyword. However, it’s not like that and, simply put, when you have a dozen pages ranking for the same keyword, you’re actually competing with yourself.