A Petty Cash book is basically a book that is kept for keeping a record of the Petty cash available to a department or a company. It records the day to day transactions done by utilizing the Petty cash account.
Actually every company keeps Petty cash. Petty cash is the small amount of cash in hand. This amount is allocated for any emergency expense or for daily routine buys. Such as purchase of tea, stationery, traveling etc. This way the company does not have to get their money out of the banks each day.