A wildcard certificate is a public key certificate

Public key certificate

In cryptography, a public key certificate is an electronic document which uses a digital signature to bind a public key with an identity — information such as the name of a person or an organization, their address, and so forth...

 with which you can secure multiple subdomain

Subdomain

In the Domain Name System hierarchy, a subdomain is a domain that is part of a larger domain.- Overview :The Domain Name System has a tree structure or hierarchy, with each node on the tree being a domain name. A subdomain is a domain that is part of a larger domain, the only domain that is not...

s.

Depending on the number of subdomains an advantage could be that it saves money and also could be more convenient.

Limitation

Only a single level of subdomain

Subdomain

In the Domain Name System hierarchy, a subdomain is a domain that is part of a larger domain.- Overview :The Domain Name System has a tree structure or hierarchy, with each node on the tree being a domain name. A subdomain is a domain that is part of a larger domain, the only domain that is not...

matching is supported.

It is not possible to get a wildcard for an Extended Validation Certificate. A workaround could be to add every virtual host name in the subjectAltName extension.
The major problem being that the certificate needs to be reissued whenever a new virtual server is added. Thus all certificates need to be replaced every time.

Example

An example of the use of a *.company.com wildcard could be:

payment.company.com, contact.company.com, subscribe.company.com, login.company.com, etc.

But it is not possible to also secure fourth.payment.company.com with the same wildcard certificate.