User Agent

What is a user agent?

A user agent identifies your browser and provides certain system details to servers hosting the websites you visit in a string. This string indicates which browser you're using, its version number, and details about your system, such as operating system and version.

E.g.: User Agent  47.37.146.138 (USA) Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.75 Safari/537.36

47.37.146.138 - shows the ip address of the user

USA - the country associated with the IP

Mozilla/5.0 - application name and version

Macintosh; Intel Mac OS X 10_12_6 - the operating system and version.

AppleWebKit/537.36 (KHTML, like Gecko) - webkit based browser using engine version 537.36 that behaves uses KHTML engine that behaves like Gecko 

Chrome/62.0.3202.75 Safari/537.36 - web browser used by user was Google Chrome 62, which is also compatible with Safari version 537.36

This is a handy tool to understand your browser's user agent string: https://developers.whatismybrowser.com/useragents/parse/

To understand more about the components in the string, see this wikipedia article: https://en.wikipedia.org/wiki/User_agent