An optional tag specified when a task is started. For example if you automatically trigger a task to run a batch process job, you could apply a unique identifier for that job to your task with the startedBy parameter. You can then identify which tasks belong to that job by filtering the results of a ListTasks call with the startedBy value. Up to 36 letters (uppercase and lowercase), numbers, hyphens, and underscores are allowed.
If a task is started by an Amazon ECS service, then the startedBy parameter contains the deployment ID of the service that starts it.