GCLID is Google Click Identifier, a tracking parameter used to connect ad clicks to conversions and offline imports.
It matters because paid search can spend budget quickly. Knowing this term helps teams control intent, targeting, bidding, creative, conversion tracking, and lead quality instead of optimizing for surface-level clicks.
Example
Example: A lead may click a Google ad, submit a form, and close two weeks later. Capturing the GCLID lets the advertiser import that offline sale back into Google Ads.