Keyword cannibalization occurs when two or more subpages are optimized for the same or very similar keywords. As a result, both pages can slow each other down and rank worse in Google search results than they actually could. In addition, keyword cannibalization can make the ranking of both pages very erratic.
A remedy is a concretization of the keywords. If this is not possible because the pages are thematically too similar, a 301 redirect to one of the two pages can be set up to bundle the traffic. This also clearly communicates to Google which of the two is the main page and should be included in the ranking.