When we visit, somepopularsite.com, we have some trust on that site. We know that it is not a malicious website or a not fake one.
If we see URL like
We see the domain, and from that, we understood, its
But, what if this URL redirects to
If redirected, then this is Open Redirect Vulnerability on facebook.com (Yes! This was an actual bug found on Facebook by @dwi.siswanto98 in Jan 2020)
Open Redirect Vulnerability can be classified as,