What is difference between HostWeb and APP Web in SharePoint 2013

All your SharePoint components should be Deployed in a separate SharePoint site, called as the App Web. The Host Web is nothing but the SharePoint site where the App is actually Installed.

Host web and App web come into picture when we are developing and hosting the SharePoint Add-in. The Host web itself suggest that it is allowing to host anything within it. So the SharePoint site where the Add-in is basically installed is called as Host Web while the URL of the SharePoint add-in is called as App Web.

HostWeb is the URL where the App is installed. AppWeb is the App URL which is created on installing an App. An App is basically a WEB