what does "DIRECTLY DEPOSITED BY A CUSTOMER - Rs.2,000" means ??.... customer directly deposited money in cash book or in the bank ??

It means that a customer has directly paid or deposited the amount into an account holder's bank account. In such cases, as the bank amount is getting increased (and accordingly the bank's pass book reflects the increased bank amount), but this remains unnoticed by the account holder. Consequently, the account holder does not record this transaction in his cash book. The next time, when he visits the bank, then he comes to know that the customer has deposited the required amount in his bank account. Thus, in this way, there exists a difference between the pass book and cash book balances. 

If in a question, balance as per cash book has been given, then we need to add the amount Rs 2000 (amount paid by the customer directly in the bank account). This is simply because the balance as per the passbook already stands increased but the same amount has not been considered in the cash book.