Finding the reasons between cash book and poss book is called
as reconsiliaton as per BRS. Bank reconsiliation statement.

Bank Reconsilation statement is the statement in which we 
have to reconcile the two balance's balance as per cash 
book and balance as per bank pass book.The purpose of 
preparing such a statement is to find out the cause of 
difference betbeen two balance's and pass correcting and 
adjusting entrie's in the books of firm.

reconciliation is nothing but it is the difference between
two balances which are cash book and pass book .this
transaction mainly done between bank and customer .the main
purpose to create brs is to make  both cash and pass book
balances are equal.