A wildcard SSL certificate is a type of digital certificate that secures a domain and all its subdomains with a single certificate. It allows for secure communication over HTTPS (Hypertext Transfer Protocol Secure) by encrypting the data transmitted between a web server and a user's browser. Typically, an SSL certificate is issued for a specific domain name (e.g., www.example.com), and it only secures that particular domain. However, a wildcard SSL certificate expands the coverage to all subdomains of a specific domain. The subdomains can be dynamically created without the need to obtain and manage separate SSL certificates for each subdomain. The wildcard character () is used as a placeholder in the certificate's common name (CN) field, representing any subdomain of the base domain. For example, a wildcard SSL certificate issued for ".example.com" would secure subdomains like "mail.example.com," "blog.example.com," "shop.example.com," and so on.