One of our sites got a Group named "Hub Visitors" what is this sharepoint group

I have created the following sites hierarchy :-

DMS
    Departments (linked to DMS Hub) 
            Learning (linked to Departments hub)
                      Communication and Privacy (linked to Learning hub)
                      Learner Support (linked to Learning hub)
                      Learning Partnerships and Standards (linked to Learning hub)
            Pre-Professional Education (linked to Departments hub)
                      Transcript Assessment (linked to Pre-Professional Education hub)
                      Strategic Innovation (linked to Pre-Professional Education hub)

but specifically on the Strategic Innovation, i got this sharepoint group created automaitcally for us:-

so what is this site and why we only got it inside a single site our of 9 sites we have created?

Thanks