Beam
In plain terms
A unified model for batch and streaming data processing.
Going deeper
Apache Beam lets you write data pipelines once and run them on multiple engines (Spark, Flink, Dataflow). It abstracts over execution engines.
Under the hood
One programming model for both batch and streaming; runners execute it on different backends.
Examples
Portable pipelines, batch+streaming, Google Dataflow, runner abstraction, ETL.
Think of it like...
Like writing one recipe that any compatible kitchen (engine) can cook.