Do you want to move a XenForo forum from a subdomain (like say forum.yourdomain.com) to the root domain (yourdomain.com)? The process is fairly simple and easy to follow. Here is a complete step by step guide.
Forums URL
What is Route – Customize Route Filters For Better XenForo Forum Urls
A route is the first part of the URL to determine the XenForo controller. It is independent of SEO friendliness or the secondary portion of the URL.