Bird’s eye view:

Oracle Applications is a collection of business Enterprise Resource Planning applications developed by Oracle Corporation, which use their core RDBM database technology, mainly referred to as Oracles "E-Business Suite".
As said above APPS is a collection of different APPLICATIONS. The first question comes what are the different applications that come under the roof of Oracle Applications.
Let me ask you one question before we start which I am sure you will be able to answer it and which in turn is the answer for above question.
Forget about Oracle Application at all and let’s imagine you are running a shop of mobile phones. You predicted that you will require at least 1000 different phones for the month ahead.
What do you do?
Yes!! you buy it from your supplier.

Think of a supplier, like you there will be 100 more shop owners who need mobile phones.
Here come the basic cycle of any business.

1. Demand is placed from customer like you.
2. This is nothing but a sale for the supplier.
3. Supplier will plan for the production of the product for the quantity required.
4. Here comes the material management in picture.
5. Once the production is complete these products are to be packed and dispatched to the customers like you who ordered for the bulk quantity.
6. Once you get the required quantity of phone, you will pay the supplier.

Now each of these phases is nothing but an individual application which all together forms Oracle Applications "E-Business Suite".

Like for demand and supply you have ORACLE ORDER MANAGEMENT (OM).
For PRODUCTION of GOODS you have ORACLE WORK IN PROGRESS (WIP).
For MATERIAL MANAGEMENT you have ORACLE BILL OF MATERIAL (BOM) and ORACLE INVENTORY (INV).
For purchasing you have ORACLE PURCHASE ORDER (PO).
For dispatch of goods to customer you have ORACLE SHIPPING.
And for taking care of finance you have ORACLE GENERAL LEDGER (OM), ORACLE RECEIVABLE (OM), ORACLE PAYABLE (AP).

I think this will give you a brief idea what we are dealing with.....