What dclid actually is
dclid, the DoubleClick Click Identifier, comes from Google's display and video advertising stack, Campaign Manager 360 and Display & Video 360, not from Google Ads search campaigns. As part of what Google calls enhanced attribution, it is appended automatically to the landing page URL on a display or video ad click, and a Google tag on that page reads it the same way it reads a gclid, so Campaign Manager can join the conversion back to the exact impression and click that led to it.
Why it's the display-side equivalent, not a duplicate
It's tempting to treat dclid as just gclid with a different name, but the two cover different inventory. gclid comes from a click on a Google Ads search, shopping or Performance Max ad. dclid comes from a click on display or video creative served and measured through Campaign Manager 360 or DV360. A campaign running both search and programmatic display produces both parameters, on different clicks, feeding two related but separate parts of the same advertiser's measurement stack. YouTube ad views specifically are measured through a different path and don't carry dclid the way a display banner click does.
Is it safe to remove?
A visitor notices nothing missing without it. For the campaign it belongs to, removing it in a redirect or a shared link breaks the join between the click and whatever conversion follows, the same failure mode as stripping a gclid. Enhanced attribution also depends on the publisher serving the ad having enabled the right consent signals, so dclid can be absent from a click even when everything else is configured correctly, simply because that particular ad placement didn't have consent to attach it.