For a particular site if you check how many pages are indexed in a search engine by “site: xyz.com”, In SERP result you will found that 50% more pages are being indexed these extra pages are called “Zombie Pages”.
By eliminating these over-indexed pages can get you a lot more organic traffic. Simply speaking the less the pages you have, the less the problem you need to face.
2.Mostly seen Zombie Pages:
Pages with Thin content
Search result pages
Category and tag pages
By using Google search console you can disavow those particular links.
By using Robots.txt you can disallow those particular links.
By using a sitemap, you can remove those links if those particular links are present in your site.
Use those over-indexed pages to your benefit, find those particular zombie pages and merge to the main site which is been properly indexed and also has organic traffic.