Both cash budget and regular budget are different. Both are estimates that are proposed for the future duration, be it a month or a year.
Cash budget is related to cash / currency (in liquid form) for daily/weekly expenses -- how much currency is to be maintained with the accounts dept. (or SB A/C in liquid form) for payments. Also cash/payments received in liquid form are part of these. Depending on the time of the year (like festivals or other days or beginning of the month), the cash budget varies. Usually further approvals may not be required for the cash budget.
Keeping too much of assets in cash or liquid form will not be productive, as that money could be used in productive activities. Keeping too less will hinder the activities.
Budget is done for allocation of expenditures for various purposes over the next year. They need not be in cash. Further approvals are required for each project or activity later on. These are the estimations of incomes and expenditures under various categories over the next one year. Often the amounts allocated in the budget are released in phases for each activity.