Difference between Org_id ,organization_id and operating_unit

For instance let us say you are having Inventory Store.
You have Inventory Stores in two different countries like India and USA
You have installed Oracle Apps single instance and entered all the suppliers information,customers data,tax rules etc.

And your business requirement is like this, all the rules and the data corresponding to indian store shouldnt be applicable/available to american store and vice versa.

So to meet the above requirements you will define two operating units one for india and one for USA.
Now each operating unit will have an ID known as ORG ID.

And we use ORG ID to secure our business data.

Now to do transactions for indian operations you need to define one responsibility and attach indian ORG ID to this responsibility.By this an indian will not see any data/rules applicable to USA.

Similarly you will define another responsibility for USA and attach USA's ORG ID to this responsibility so that an american will not see any data/rules corresponding to India.

This is the concept of ORG ID.

Now let us see what is Organization ID.

Within India you have got various branches in different parts of the country in different states like AP,UP,MP etc.
And the business requirement is like this in AP you will maintain stock of Rice,UP for Wheat and MP for Maize.
To meet this business requirement you will define 3 Inventory Organizations under Indian Operating Unit to maintain the respective stocks of the states..

Each Inventory Organization will have an Organization ID.

This is the outline of the differences between ORG ID and Organization ID.