A Flex SSL certificate is a type of SSL/TLS certificate that offers enhanced flexibility in securing a website's domain and subdomains, unlike traditional SSL certificates that are strictly issued to a single domain, a set of specified domains (Multi-Domain), or all subdomains under a single domain (Wildcard), a Flex SSL certificate allows for a mix of these configurations. This means you can secure multiple specific domains and any number of their subdomains under one certificate. For example, with a Flex SSL certificate, you can secure www.example.com, mail.example.com, example.net, and blog.example.net, all with a single certificate. This flexibility makes managing SSL certificates for a website or a group of websites much simpler and more cost-effective, especially for businesses or individuals who operate multiple sites across different domains and subdomains.