What does fbclid tell a web site?

If I reach a web site through a link from Facebook, Facebook tacks on a parameter to the URL like this:

fbclid=IwAR3tB20k54fz_p66ZfsNttm8QlXTip7bRvDlGGpM3WT-JACCNKtEZ4Ci5Fs

Aside from telling the web site that the user came from a Facebook link, what other information is provided in the code?

I don’t think you’re going to get an answer. Facebook seems to be keeping that information secret. Here is a web site set up to give information about it by interested parties, and it’s pretty sparse:

I can tell you that fbclid stands for “Facebook Click Identifier”.

That web site promises to add more information if and when more info comes out from Facebook or those analyzing it.