Multi-Org or Multiple Organization Access (MOAC) in R12

What is MOAC?
Multi-Org or multiple organization access (MOAC) is basically an ability to access multiple operating units from a single application responsibility.

Why it has been created?
Prior to R12, end users use to toggle / switch / change responsibilities in order to do transactions (like invoice / payment processing in AP) in different operating units. This is a very time consuming and inefficient way of recording transactions when you have 100s of operating units specially Internet based organizations who have worldwide operations in almost all the countries. To address this, a new feature in R12 has been introduced in which user can switch between operating units within a responsibility something similar to “Change Organization” feature in inventory. Prior to R12, user would have to switch responsibilities in order to enter transactions in respective operating units (tagged to the responsibility).

What are its advantages?
Multi-Org Access Control (MOAC) enables companies that have implemented a Shared Services operating model to efficiently process business transactions by allowing them to access, process and report on data for an unlimited number of operating units within a single applications responsibility.
This increases the productivity of Shared Service Centers, as users no longer have to switch application responsibilities when processing transactions for multiple operating units at a time.
Ability to view data from multiple operating units from a single responsibility, gives users more information. This enables them to make better decisions.
The following SQL will dump out the Security Profiles and Operating Unit Names assigned to them.

SELECT   psp.SECURITY_PROFILE_NAME,
         psp.SECURITY_PROFILE_ID,
         hou.NAME,
         hou.ORGANIZATION_ID
FROM     PER_SECURITY_PROFILES psp,
         PER_SECURITY_ORGANIZATIONS pso,
         HR_OPERATING_UNITS hou
WHERE    pso.SECURITY_PROFILE_ID = psp.SECURITY_PROFILE_ID
         AND pso.ORGANIZATION_ID = hou.ORGANIZATION_ID;
There are three Profile Options you need to be aware of related to Multi-Org that should be set at the Responsibility Level.
MO: Security Profile- Always evaluated first.
MO: Operating Unit- Secondary priority being evaluated after ‘MO: Security Profile’
MO: Default Operating Unit- Sets the default Operating Unit for transactions when running under a Security Profile.

How it is done in R12?
In Release 12, one creates a Security Profile and assigns as many operating units as you required. One can tie that security profile to a single responsibility using a profile option called MO: Security Profile. For example, you could assign the security profile to the EMEA Payables responsibility to allow that responsibility to process invoices across all operating units.
In Release 12, define a security profile in HR using the Security profile form or the Global Security profile form, and assign all of the operating units that one would want a responsibility to access. The one needs to run a concurrent request called “Run Security List Maintenance” from HR which will make those security profile available and allow one to assign them to a responsibility via a profile option called MO: Security Profile.
One can define another profile option called MO: Default Operating Unit which is optional and allows one to specify a default operating unit that will be the default when you open different subledger application forms.

References:
http://amaralam.blogspot.com/2013/04/what-is-moac-multi-org-or-multiple.html