When an operation can be performed concurrently on source collection elements, it is referred to as data parallelism. In this process, the source collection is partitioned into multiple threads and executed in parallel. .NET Framework supports data parallelism via the System.Threading.Tasks.Parallel class. Methods such as Parallel.For and Parallel.ForEach are defined in this class. When you use these methods, the framework manages all the low-level work for us. 

A task represents an asynchronous operation and does not return a value. These are defined in the System.Threading.Tasks class.