Hi Nagarajan
Yes terminology can be used interchangeably. Also, some people refer to logical components as separate (i.e CUA - event though that is an ALE model - in some cases it is set up as own system, whilst others it is part of ERP).
Keeping it simple and back in line with this particular thread: You connect multiple systems to GRC. Each of those connections has it's own user repository. In the case of an ABAP system, the user repository are the SU01 User Accounts.
As users get access to different systems (which happen to be a specific component) they will have SU01 accounts existing in different places to each other. In GRC, we connect them all to maintain centrally and therefore, define our data source to look at all the places. So if a user was using End User Login screen, they could login with their SAP ECC or CRM password ,etc - assuming the data source was configured that way.
Does this clarify your questions or are you still unsure?
Regards
Colleen