SAN, UCC, and "multi-domain" get used as if they're three different products. They mostly aren't. Underneath, they all rely on the same mechanism — they just come from different naming traditions. Here's how they actually relate, so you can read a product page without getting confused.
SAN: the field, not a product
SAN stands for Subject Alternative Name. It's a field inside a certificate that lists every name the certificate is valid for. A certificate with a SAN field can secure several names at once — example.com, www.example.com, mail.example.com, and even entirely different domains.
So SAN isn't really a "type" of certificate. It's the part of the certificate that makes covering multiple names possible in the first place.
Multi-Domain: the marketing name
"Multi-domain certificate" is the plain-language label vendors use for a certificate that uses the SAN field to cover multiple domains. When you see "multi-domain SSL," you're looking at a SAN certificate described by what it does rather than by its technical field name.
UCC: the same thing, from a different world
UCC stands for Unified Communications Certificate. The name came from Microsoft Exchange and Office Communications environments, where one server needs to present several hostnames. Technically, a UCC is a multi-domain (SAN) certificate — the term just signals it's positioned for those communication-server use cases.
How this differs from wildcard
People often weigh multi-domain against wildcard, so it's worth being precise:
- Multi-domain (SAN/UCC): covers a fixed list of specific names you choose, which can be different domains.
- Wildcard: covers one domain plus all its first-level subdomains (*.example.com), but only one base domain.
If you need several distinct domains, multi-domain fits. If you need many subdomains under one domain, wildcard fits. Some setups combine both.
| Term | What it is | Covers |
|---|---|---|
| SAN | A field in the certificate | Multiple listed names |
| Multi-Domain | Marketing name for a SAN cert | Several chosen domains |
| UCC | SAN cert for comms servers | Several hostnames/domains |
| Wildcard | Single-domain subdomain cover | *.one-domain.com |
Which should you ask for?
Don't get hung up on the label. Decide by what you're securing: a set of specific, separate names points you to a multi-domain (SAN/UCC) certificate; a single domain with lots of subdomains points you to wildcard. The wizard turns that into a concrete SSL.com recommendation.
SAN, UCC, and multi-domain aren't three products — they're three names for using one field.