Speculation is applying logic to what is known without really knowing (or needing to know) what Universal is doing. It’s an educated guess.
A rumor means someone has been told something IS occurring by a source that can be traced to those who know what IS happening. It’s a game of telephone.
Saying “Universal is doing Hereditary because it was a popular movie,” is speculation. Saying, “I’ve heard Universal is in negotiations for Game of Thrones,” is a rumor.
There’s a bit of a schedule to this, too. Between August and January, chatter is predominantly speculation. Rumors exists, but most rumor mongers are fairly tight-lipped about them because it’s really too early to validate anything. February-March is when rumors start locking in.
My clues are coming early this year because I’m not doing the work filter out bad info. I’m doing clues for rumors I can source. I’ve “heard” 6-7 rumored IPs (including Doctor Who), plus some other information, and I suspect maybe half are accurate.