A sensor in PRTG speech is defined as one aspect that you can monitor on a device, such as the CPU load on a machine, a port of a switch, a specific URL or the traffic of a network connection. See this list for more sensor types.
A PRTG server is the central unit of PRTG. It receives monitoring data from the probe and handles reporting and notifications, provides the web server for the user interfaces, and much more. Read more