A budget is a plan for projected income and expenses over a defined period. Budgeting involves formulating budgets, while budgetary control uses budgets to plan and control all aspects of production. Key elements of budgetary control include preparing budgets for each department, conducting ongoing comparisons of actual vs. budgeted performance, and taking corrective actions on variances. Budgets can be classified by time period (long-term vs. short-term), function (sales, production, etc.), or flexibility (fixed vs. flexible). Zero-based budgeting requires justifying all expenses for each new period without relying on previous budgets.