www is subdomain that was exposed to the wider internet in the times when people have had an internal network that mattered a.k.a at the times of only big corpo

www is subdomain that was exposed to the wider internet in the times when people have had an internal network that mattered a.k.a at the times of only big corporations having internet at all. So, a corp.inc might've been the internal portal for the workers, while www.corp.inc was the public facingg page of the company.