Outbound links are links inside your website that point to external websites[if you are www.xdomain.com you have a link pointing to www.ydomain.com] Inbound links are links from external websites pointing to yours[www.ydomain.com pointing to www.xdomain.com
Outbound links = someones website link on your site Inbound links = your link on someones website Hope now its clear with you...
I guess, you are new in SEO? Inbound links refer to the number of links incoming from external sites and outbound links refer to the links outgoing to another sites from your site itself.