Description
rb_clickid was added as a tracking parameter in jparise/chrome-utm-stripper#44, but it's very hard to find any information about it (note that we should leave linkid alone for webcompat reasons).
It's used all over the place on Russian sites, for example:
https://veryberrylab.ru/catalog/bukety-s-klubnikoy/?rb_clickid=86252549-1618003652-1663225310&size=1&price_from=3000&price_to=5000
A lot of Russian websites also exclude it in their robots.txt, for example https://esh-derevenskoe.ru/robots.txt.
The TopMailRu tracker does seem to use it, though their minified code is especially hard to decipher.
The only blog post I could find about it only mentions that it's often seen in combination with utm_source=mytarget though the example above shows that it's not always the case.
Based on its name and the fact that it's high-entropy, we should assume that this is tracking users as opposed to campaigns.