A modifier function is a coding function used primarily in smart contracts and decentralized applications. Its primary role is to modify the input or behavior of other functions, usually to enforce rules or conditions.For example, a modifier can restrict access to certain functions based on user authorization. This ensures that only designated users can perform sensitive actions, like transferring funds or altering contract parameters.Modifier functions can also be used to validate input data. They check that the data meets specific criteria before a function is executed, enhancing the security and reliability of the contract.In addition, they can help manage gas costs. By consolidating repetitive checks into a modifier, the overall efficiency of the contract can be improved, as repeated code is minimized.Using modifier functions promotes cleaner and more maintainable code. By separating concerns and allowing for easy updates, developers can enhance the functionality of the contract without disrupting existing processes.