Understanding SharePoint Security Scope

Question

What is a Security scope in Sharepoint?
a) Number of times we break inheritance
or
b) each time you grant access to a new principal (user account or group) then you are creating a new Security Scope?

Answer 1

Sonal
Security Scope is just a term used to describe a situation - it has no physical significance, meaning, it is not a specific setting that you configure. 
For example, if I create new security groups for a site, and grant them some permission level (eg, Contribute, Read, etc), then I have effectively configured the "Security Scope" for that site.  If I create a subsite off of this
one, break its permissions inheritance, and configure new groups for it, I have effectively configured its "Security Scope".  If I now create a list in this subsite, add some items, break the list's permissions inheritance from the subsite,
and configure some users or groups for accessing this list, I have effectively configured the list's "Security Scope." Thus, "Security Scope" is a term that describes boundaries, so to speak.
The key thing here is how the "Scope" of a security configuration, such as granting a user or group some permission, narrows as you go from doing this for a site down to doing this for a list or even a list item.  A user or group that is granted
permission to read only a single item in a list can only see that one item in the list and cannot see anything else.  Nor does that permission enable the user or group to read list items in other lists.  Thus, the "Scope"
of that security settings is very narrow.