A Multi-Domain SSL certificate can secure your main domain along with several SANs (Subject Alternative Names) domain names in one certificate.
Multi-Domain certificates are often used for Unified Communications (UC) to secure Microsoft Exchange 2010 Server, Office Communications Server 2007 or Mobile Device Manager.
For example, you can secure all these domains with a single Multi-Domain certificate:
www.namecheap.com
www.exchange.namecheap.com
www.namecheapgroup.com
Note that www and non-www versions of one website are considered as two different hostnames, so if you would like to secure both www and non-www versions of one website, it will be necessary to specify both of them in the list of SANs.
Multi-Domain SSL certificates do not require several dedicated IP addresses for your host names.
