Multi-Org or multiple organization access (MOAC) is basically an ability to access multiple operating units from a single application responsibility. MOAC in r12 technical is the great feature in Oracle Apps.
In 11i, end users must change the responsibilities to do transactions 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 like “Change Organization” feature in inventory. Prior to R12, user would have to switch responsibilities to enter transactions in respective operating units.