Subdomains in Binder are personalized URLs linked to your account (e.g., yourcompany.binder.so). They help maintain a professional appearance and branding when sharing documents or creating data rooms. Remember that using subdomains means that your primary domain remains binder.so. If you prefer to use your custom domain instead of binder.so, you can easily set one up.
Here is a guide on how to setup custom Domains with Binder, click here