What feature is required to send data from a web-connected device (like a point-of-sale system) to Google Analytics?

The Measurement protocol is a standard set of rules for collecting and sending hits from any internet-connected device to Analytics. The Measurement Protocol lets you send data to Analytics from any internet-connected device. It's particularly useful when you want to send data to Analytics from a kiosk, a point of sale system, or anything that is not a website or mobile app. Because, while the Analytics JavaScript and mobile SDKs automatically build hits to send data to Analytics from websites and mobile apps, you must manually build data collection hits for other kinds of devices. The Measurement Protocol defines how to construct the hits and how to send them to Analytics.