Answer: Triggers

Triggers are the mechanism that determines when the elements for a specific key and window should be output. Upon arrival, elements are placed into one or more windows by a Window transform and its associated WindowFn. The Trigger then decides if the window's contents meet the criteria for output. For more details, refer to the [Google Cloud Dataflow documentation](https://cloud.google.com/dataflow/java-sdk/JavaDoc/com/google/cloud/dataflow/sdk/transforms/windowing/Trigger).

Author: LeetQuiz Editorial Team