cost object

A customer can be considered as a cost object. I do not know where you read differently, but if it did read differently then it was wrong. A cost object is simply something/someone that you measure the costs for. It is up to the particular business to decide what to measure the costs for - there is no rule - it could be the customer, it could be a manager, it could be a product, it could be a machine etc..

Thanx john sir i got it.

You are welcome :-)

what is the difference between a cost unit and a cost object?

They are basically the same. A cost object is whatever it is that we are costing. A cost unit is a cost object but is more the situation when we are actually producing things. (A cost object could also be things like a customer.)