Some people get confused, because they hear about "back links", "in bound links", "whatever link" lol. We were all new once.
One way link is a link which has pointed to someone else linked, web page or website without providing link back. It is the best technique in search engine optimization. In search engine optimization no. Off techniques provide the one way link like directory submission, social bookmarking, article submission and many more.
One way link building helps you to get both traffic and higher page ranks of your site of blog. But it is going to be some wasted efforts if you don't understand how this works and how it will help to boost your entire online presence.
One way links are more powerful and it's when other sites link back to you but you don't. Two way links is when site A links to site B and site B links back to site A. Webmaster used to use two way link building long time ago before search engines were there. Now 2 way links are not as powerful as one-way links and are sometimes frown at by the search engines if you don't know how to do it properly.