A Credit Control Area is an organisational unit that is 
compraised of one or more company codes.A company code can 
have no more than one credit control area.

outstanding recievables can spoil the business process. to 
control credit limits in sap system we can configure credit 
control area. 
one company code can hav one credit control area only 
but one credit control area can hav many company codes
i.e. u can assign one credit control area to many company 
codes.
the relationship is one to many

all the above answers are absolutely right 

In my point of view 
CCA  is the area where one can enter the amount.

ex: amount is 15,000

Now ,customer makes an order of 14,000 price of materials 

then the order is created.

in a case customer  makes  an order of 16,000 price of 
materials
the system will generate an error saying customer CCA is 
reached.


if i am wrong please correct me.

Credit control area is an organizational unit which checks
the credit limit of the customer .One credit control area
can include more company codes .That means the relation is
one to many .

Thanks
manoj