A vanity URL is an address branded for the purpose of marketing promotion. Vanity URLs are short, easy to remember, and often contain a call-to-action phrase. They can be set up to redirect the visitors to a longer, harder to memorize URL.
The main reason for creating vanity URLs is to ensure consistent branding. Companies may decide to create this type of URLs using their main domain, or to purchase a shorter domain specifically for this purpose. Some online services enable their users to create vanity URLs using either the default domain of the service or their own custom domain.