UCC – Unified communications certificate also known as SAN can be used to secure a number of domain names and sub-domains using one certificate.
For example you can use these to secure:
How does this differ from a wildcard certificate?
Wildcard certs can only be used to protect unlimited numbers of sub-domains off of one domain name, they cannot be use for different domain names.
This type of certificate would be needed in an environment where you need to secure multiple names across different domains.
How many domains can be covered by a UCC?
This depends on the level you purchase. They typically will include 4-5 domains but all SSL vendors offer higher level UCC for larger environments.