Just curious...
'm just stating the astronomical definition of a group of star systems in close proximity, friend. The astronomy textbooks don't care what the programmers call it, and neither do I.
Now, given that a group of stars is called a cluster as you stated, and and individual star with it's planets is a system (is that correct?), if you had 40 stars in a cluster, and broke those down into groups of 10, you would have 4 sectors. Sort of like the idea of 2 cities being geographically close, in the same state, but in different counties.
So perhaps a hypothetical Sol sector would be a group of stars in the cluster including the stars of the "Sirius Sector" etc.
Just wondering. Most of this is above my head anywho.