Backlinking is the technique of search engine optimization by which you used to put the link/hyperlink of your website on other's website. It is nothing but the inbound link. The links are from your own site to other site and back to your own site that is why it is called as back-linking. Backlinks are important for SEO because some search engines, especially Google, will give more credit to websites that have a good number of quality backlinks, and consider those websites more relevant than others in their results pages for a search query.
Back-link will helps bots to to discover your website and crawl your website effectively. If your website is new then due to back-liking, it helps indexing your website very fast.