What is "subdomain"
Subdomain are the branches of the main domain, something widely used in large websites. On the [support.youdomain.com.br], for example, [www.seudomain.com.br] is the domain, and "support" is the subdomain, which has the function of driving the user directly to the specific section of the site.
When this function is used, it serves to facilitate domain maintenance by easily identifying the services available to those who will access the domain. For example: forum.seudominio.com.br, chat.seudominio.com.br, mail.seudominio.com.br.