A Stream in Java 8 can be defined as a sequence of elements from a source. Streams supports aggregate operations on the elements. The source of elements can be Collection or Array that provides data to the Stream.
Stream keeps the ordering of the elements the same as the ordering in the source. The aggregate operations are operations that manipulate stream elements quickly and clearly.
Java Parallel Streams is a feature of Java 8 and higher. Normally any java code has one stream of processing, where it is executed sequentially. But by using parallel streams, we can divide the code into multiple streams that are executed in parallel on separate cores