What tblci actually identifies
Taboola sets tblci the moment you click a thumbnail inside one of its widgets: the "around the web," "you may like," or "recommended for you" boxes wedged into the bottom or sidebar of a news article. The value is a click identifier. It points at one specific click event inside Taboola's ad network, not at you as a person and not at your device across visits. Two people clicking the same thumbnail seconds apart get two different tblci values.
When it gets attached, and by whom
The parameter is added by Taboola's own redirect server, not by the publisher's site and not by the advertiser's site. Click the thumbnail and your browser first lands on a Taboola tracking domain, which logs the click, then forwards you to the advertiser's landing page with tblci appended to the destination URL. That bounce happens in milliseconds. You will sometimes see the same value appear twice in one link, once in the query string and again packed into the fragment after the #. That doubling is normal for Taboola's redirect pages.
What disappears if you cut it out
For you as the visitor, nothing changes. The landing page renders the same article or offer with or without tblci, because the parameter carries tracking data rather than page logic. For the advertiser who paid for that click, it is different. Losing tblci, whether you delete it by hand or an ad blocker strips it before the redirect fires, means Taboola's Backstage platform can no longer tie the resulting pageview back to the widget placement, article, or campaign that produced it. That click drops out of the campaign's performance numbers.
Reading the token itself
A real tblci value reads as a long run of lowercase letters and numbers, often starting with a short prefix like Gi, with no readable words anywhere in it. Treat it as case-sensitive: it is an opaque lookup key, not a word you would retype from memory. There is no way to decode it into a campaign name or article title yourself. It only means something inside Taboola's own systems, so it is useless to anyone without account access to that campaign.
Taboola is one of several networks running these recommendation widgets. Outbrain's version works differently: its parameter, obOrigUrl, carries an entire second URL as its value rather than an opaque token. If your strange parameter came from a search ad instead of a content widget, check yclid, or browse the full link decoder list.