This document discusses Java 8 streams and how they are implemented under the hood. Streams use a pipeline concept where the output of one unit becomes the input of the next. Streams are built on functional interfaces and lambdas introduced in Java 8. Spliterators play an important role in enabling parallel processing of streams by splitting data sources into multiple chunks that can be processed independently in parallel. The reference pipeline implementation uses a linked list of processing stages to represent the stream operations and evaluates whether operations can be parallelized to take advantage of multiple threads or cores.