Main different between outbound link or inbound link?

Well, I guess from the term everything clears up Outbound Link: They are links going out of your site, like you have a website (you share information about various business sites to user) you add site over to your site not your site is pointing, it's termed as outbound link.
Inbound Link: They are the links coming over your site like sees that you have added them over their list and they write a post about it in their blog and add your site referece over, (say) now such type of links are termed as inbound link.