The Unified Communications Certificate (commonly known as UC certificate, UCC certificate or SANS certificate) is a multi-domain SSL certificate that can secure up to 2000 domains. This is accomplished through the Subject Alternative Name (SAN) field, and browsers check this field for a matching domain or IP address to one in the address bar.
Since an SSL certificate binds to a single IP address, UCC is ideal for environments when multiple domain names, internal as well as global, need to be shared in a single SSL certificate such as Microsoft Exchange (OWA, Outlook Anywhere, ActiveSync, Autodiscovery, and SMTP) or Office Communications Server 2007. It also works great in virtual hosting environments or where multiple sites need to share a single IP address like in Amazon’s EC2 cloud