Business Rules are like trigger. They run only when an action occurs on the record. There are different types of Business Rule. One of the Business Rules is called Async. The async business rule can run when record is inserted or updated and runs asynchronously. So it doesn't hold the UI while executing.
A scheduled job is like a job that you would want to occur on a certain time repeatedly.
For ex, you want a report of all tickets assigned to a team to be sent to the team. You can setup a scheduled job for that. Or you want to run a script Daily or weekly to create some records or update some data, you can use scheduled job
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