"What Are Business Rules"

"What are Business Rules" !!! ..Though sometime it sounds a very simple term but business rules carry a real depth infact It is the core of any business,organization,corporation....
("What are Business Rules")Business rules defines
the logic,the constraints ,macro level definitions,the strategy ,infact the whole architecture of any enterprise.
("What are Business Rules")Business rules projects the processes and computing of an organization
and thus ,places all this scrambled pieces together to achieve common goals.

For example let say , there is a credit card company XYZ.For this company the business rules can be as follows :

if credit rating of a customer is 1
assign 600$ credit limit

if credit rating is 2
assign 500$ credit limit

So,here you see the business rules is set of statements that drive the business i.e. assigning a specific credit limit as per the credit rating.
("What are Business Rules").....Hope the statements above clarified this question....still it has a vast implication,I tried to narrow it down to a bit.