UA

User Agent – A user agent is any software that retrieves and presents Web content for end users or is implemented using Web technologies. User agents include Web browsers, media players, and plug-ins that help in retrieving, rendering and interacting with Web content.
The User-Agent request header is a characteristic string that lets servers and network peers identify the application, operating system, vendor, and/or version of the requesting user agent.
Example User Agent String: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.103 Safari/537.36