Enter all of your bad links now:
Backlink an external link pointing to your site from any other domain. The entire internet works based on backlinks that connects one domain to another. Without backlinks, you probably struck into a single site and your information will be limited. In addition, it is not possible for single site owner to provide all necessary details on a topic. Therefore, it is encouraged to link to creditble source so that readers on your site can get the compelte information they need.
Backlinks are good and determine the search engine ranking position of a webpage. The page with more backlinks will rank top in Google compared to a new page with lesser backlink profile. Unfortunately, this is not the end of story. The problem with backlinks is that they are out of your control. It is good when you have backlinks from high authority domains. However, it is also equally bad to have backlinks from spam websites. Sometimes, competitors can link your site in a spam site to reduce your search engine ranking. In all bad situations, you can reach out to the site owner and ask them to remove your site's link. If it is not working with email communication then the only option for you is to inform search engines to ignore the spammy links.
Here comes the use of disavow file which is a simple text file containing all spmmay backlinks to your site. You can submit this file to Google and Bing so that they will ignore the links in the file when using the algorithm for deriving search ranking.
Below is an example disavow file content for ignoring URL and domain. Use # sign for adding comments in the file.
# Remove individual Link
# Remove domain