A rule, in general, is defined as a governing power or authority. It can also be defined as a method or procedure for solving a problem.
Here, we are talking about a Business rule. If we look at its definition, it says that Business rules are the constraints which control the behavior of the business. In our case of budgeting through Hyperion Planning applications, Business rules have more to do with business calculations.
A simple example of a calculation is to compute the travel cost by multiplying the headcount with the average travel cost per resource. This simple multiplication is also a business calculation.
Another example is of allocation of costs. In budgeting cost allocation to departments, it is important to identify the cost incurred by the individual departments. Hence, we generally write Business rules for allocation also known as allocation rules.