The Gclid is a globally unique tracking parameter (Google Click Identifier) used by Google to pass information back and forth between Google Google Ads and Google Analytics.
It is enabled by turning on auto-tagging in your Google Ads account or by using the gclid parameter on the final URL suffix.

It is an extremely important parameter that allows our system to differentiate organic traffic (which doesn't have the GCLID value in the URL) from paid traffic (which does include the GCLID value in the URL)

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