Back links are also known as inbound or incoming links, and they are links to your website from another place on the internet. They are extremely useful to search engines, because they give a good indication that a website is popular. Another website adding a link to you is essentially a vote for your website, as it shows their customers that they think your site is worth visiting.
In addition to promoting your site via social media, it may be worth seeing if you can get links to your domain included anywhere else – for example, if you are a trade supply firm and the stores and tradesmen who use you have links to your website on their own sites, these backlinks will generate visitors to your site. They will also show search engines that your website is relevant to the type of people who are interested in those particular products or services.