A Unified Communications Certificate (UCC) is an SSL certificate that secures multiple domain names as well as multiple host names within a domain name. A UCC SSL certificate lets you secure a primary domain name and up to 99 additional Subject Alternative Names (SANs) with a single SSL certificate. For example you can use a UCC to protect www.domains1.com, www.domains2.net and www.domains3.org.
UCCs are compatible with shared hosting and ideal for Microsoft Exchange Server 2007, Exchange Server 2010, and Microsoft Live Communications Server. However, the site seal and certificate "Issued To" information will only list the primary domain name. Please note that any secondary hosting accounts will be listed in the certificate as well, so if you do not want sites to appear 'connected' to each other, you should not use this type of certificate.