Understand what a budget is, its importance, and the differences between balanced, surplus, and deficit budgets. Ideal for students and finance enthusiasts. A budget is a sum of money set aside and divided up to cover particular expenses. Like allotting certain amounts for food, rent, movies, and manicures every month to make sure you don't run out of cash. BUDGET definition : 1. a plan to show how much money a person or organization will earn and how much they will need or…. Learn more.