What is Link Building

Link Building is one of the most important technique or SEO skill or a part of Off-page SEO. It is the process of sharing ones link to other websites or we can say that it is the process of attaining a links to your own website from other website to increase rank of targeted keyword that have been used as a title during the process of Link Building, also it helps to increase a page rank of website in search result page and generate more traffic to website by diverting visitors to web pages.The link generated from other websites to your website are called backlinks.

Types of link Building

1. One Way Links: One way links are referred to those tactic of link building which gets those links on the site from other websites that does not have to reciprocate back. We can do this by article submission, directory submission, blog posting or posting unique content, press releases etc. These links are really important and beneficial in improving keyword rank in SERP. The best way to get these links is by posting unique content. As it provides your site a professional look and quality content that keep your readers engaged, which will increase more visitors and popularity to your site and pages and thereby, other related sites will show-up their interest with you and hence other related sites will be eager to get linked with you.
2. Two Way Links: It is the process of exchanging links between two sites, but they need to be related to the subject of your website and web pages. It is against the guidelines of Search Engine (Google) and it don not allows such linking because people can share their link with each others website who are known to each other.
3. Three Way Links: Three Way Links is a type of reciprocal linking that gets links from any website and gives a reciprocal link to any other third site. This process is also against the guidelines of Search Engine (Google) and it don not allows such linking because of the same reason mentioned in two way links as people can share their known links.
4. Automated Links: This is a process of generating backlinks from other websites automatically. Automated link services are provided by lots of websites or directories available online. You can get links exchanged by simply getting membership on a site that exchanges group links but keeping one thing in mind that Search Engine (Google) do not allows such strategies and if you caught you have to pay in form of heavy loss in page ranking.

Hence all those links which comes and are directed from other websites to your websites are Backlinks.

Reference

http://theseoapps.com/seo/guide-to-link-building/