The fundamental difference between a Client Script and a Business Rule in ServiceNow lies in where they execute and when. A Client Script runs on the client side — that is, in the user ' s browser — and is primarily used to control UI behavior, validate data before submission, and enhance user interaction with forms. Client Scripts can run at different stages (onLoad, onChange, onSubmit), but they always execute within the browser environment.

A Business Rule, on the other hand, runs on the server side and executes when records are inserted, updated, deleted, or queried in the database. Business Rules are used for enforcing data integrity, automating server-side logic, and integrating with other systems. They can be set to run before or after a database action (before insert, after update, etc.).

Therefore, the correct statement is that Client Scripts execute on the client and Business Rules execute on the server.