Both contacts and leads can be found in your Lead Database. The way to discern the different between the two is by their "SFDC Type." It will either be "SFDC Type = lead" or SFDC Type = Contact."
Go to your Lead Database, click on the System Smart Lists folder. Click on All Leads. Click on the Leads tab, and then scroll to to the right side of the page where you'll see the SFDC Type.