Sometimes you need code to run automatically: every hour, every day, or on a custom schedule. That's what cron jobs do. The schedule is defined using a cron expression like 0 * * * *, which reads as "minute hour day month weekday" (this one means "at minute 0 of every hour"). Use cron for recurring tasks like fetching data, cleaning up old records, or sending reports. Combine with KV storage to cache results so you don't have to fetch them each time.