Cron jobs are a way to automate work by running scripts at regular intervals, such as every hour or daily. They use a specific syntax to specify the schedule, which includes five numbers representing minute, hour, day of month, month, and day of week. Cron uses the host machine's time zone, typically UTC, and can be used for various tasks like data jobs, sending reports or alerts, and system maintenance. However, cron has limitations, including being primarily made for shell scripts, lacking monitoring, and requiring cloud provisioning. Modal is an alternative to cron jobs that allows scheduling Python code directly with basic monitoring capabilities.