Heres examples of redirect and Masked redirect. In some services help pages its written how it works.
Where to find same functionality in Virtualmin?
https://support.godaddy.com/help/article/422/manually-forwarding-or-masking-your-domain-name
https://help.yahoo.com/kb/yahoo-domains/learn-set-domain-forwarding-sln17950.html
http://help.1and1.com/domains-c36931/manage-domains-c79822/domain-destination-c38672/create-a-url-mask-for-your-domain-frame-redirect-a693560.html