Backlink is connected between each other website or in other words it is the link from other sites pointing to your website. Backlink effect when Googlebot visited websites with links to your website which means that your website is also Googlebot visits.
More backlinks means your website is very popular in one particular field, you will be a high priority ranking in search results of your field. But note that only get links from quality websites you are offline.

Backlink Why important?

In terms of users, effective backlink user navigates to your website, it's random customers that your potential.
For SEO, Backlink also used to increase rankings. The more backlinks your website means quality, many other sites link to, so that ranking on SERP increased significantly, especially Google.