Full Path Disclosure (FPD) is a type of vulnerability that occurs when the web server, due to configuration or design errors, shows an absolute path of the system or the files where the resources of the web application are located.
 
In the following image we can see how after entering an specific website path, the absolute path is reflected in the response of the server.
 
URL: http://NETDATA:19999/Red4Sec

Another example is the following URL: http://NETDATA:19999/api/v1/alarms?active&_=1540803144140