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

[john john]

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

[#2]

This is by design to enable you to sync your Hub visitors to any site joined to the Hub so they can be visitors also there

[#3]

@Juan Carlos González Martín  but this should only happen when we sync the permissions ... but we did not sync the permissions + why this is happening on some sites only ?

Thanks