What is _ga in url path?

Question

I just opened a link which leaded me to a root (main) page of www of some Organization (let's call it XXXXXXX). It was opened from 3rd party www, not from with XXXXXXX's www.

The url in web browser has this structure:

http://www.XXXXXXX.org.pl/?_ga=1.123456789.123456789.123456789

I suspect that the ga stands for Google Analytics and the numbers enable owners of www.XXXXXXX.org.pl to check where that page was opened from, am I right?

How that "enable ... to check where that page was opened from" actually work?

Solution

This is needed for cross-domain-tracking, and yes, it stands for google analytics.

You can't stop Google from adding the tag, but you can tell Analytics to ignore it in your reports.