Plan for host-named site collections (SharePoint Server 2010)
https://technet.microsoft.com/en-us/library/cc424952.aspx
Microsoft SharePoint Server 2010 supports both path-based and host-named site collections. The primary difference between path-based and host-named site collections is that all path-based site collections in a Web application share the same host name (DNS name), and each host-named site collection in a Web application is assigned a unique DNS name.