In this article you will learn how to configure alternate access mappings in SharePoint 2013.Each of web application can be associate with a collection of mappings between internal and public URLs. Both the url’s internal and public consist of the protocol and domain portions of the full URL.
A public URL is what users can access the SharePoint site, and that URL is what appears in the links on the pages. Internal URLs is in the URL requests that sent to the SharePoint site. Many internal URLs can be associated with a single public URL it means we can use many internal URL’s for single public URL.