A jetsam event on an iPhone is a type of system diagnostic that occurs when the device runs low on memory. When this happens, the operating system terminates background applications and services to free up resources for the active application. This helps ensure that your device continues to run smoothly and prevents it from crashing due to lack of memory. To prevent jetsam events from occurring, it’s important to manage your device’s memory usage by closing unused apps, clearing out temporary files and other data regularly, and monitoring how much data each app is using.