Off page search engine optimization refers to links coming from other web pages and how those links are created. Not all links are created equal!
There are two types of incoming link;
This is where you put a link on your web page that links to another site and the other site puts a link on their site that links to you!
One Way Links
These are links that only link either too you, which is very good and what you want. Or from you, which is not so good (for you).