It appears to be distinct. A cookie prefix can impose a requirement that the cookie also have the Secure flag. So optimal security might involve using both together, but even then, the MDN example for prefixes shows the server also setting the Secure flag explicitly.
I'm not sure keyword-searching unaccompanied by research is an optimal method for correlating features to MDN data...
Presumably "secure context" refers to https://w3c.github.io/webappsec-secure-contexts/ , which is in large part about framing and workers, not just HTTPS; so I'm skeptical of any relation to cookies. But it's also unclear WTF that MDN datum is about.
But it's also unclear WTF that MDN datum is about.
That's precisely why I was asking. I was trying to correlate available compat data with the topics covered on the MDN documentation page.
A lot has changed in the realm of security since Set-Cookie was introduced and, indeed, since this issue was filed. I am merely trying to identify whether the use and support of Secure has been superseded or subsumed by another concept (such as SameSite).