Self Signed Certificate

A self signed certificate is a certificate that is signed by itself rather than a trusted third party. This means you can't verify that you are connecting to the right server because any attacker can create a self signed certificate and launch a man-in-the-middle attack.

Visitors will see a warning in their browsers when connecting to an IIS site that uses a self signed certificate until it is permanently stored in their certificate store. Never use a self signed certificate on an e-commerce site or any site that transfers valuable personal information like credit cards, social security numbers, etc.

Click on the name of the server in the Connections column on the left. Then, double-click on Server Certificates in the features view.

MSDN: Internet Information Services