Parallelism
Parallelism means that an application splits its tasks up into smaller subtasks which can be processed in parallel, for instance on multiple CPUs at the exact same time.
To achieve true parallelism your application must have more than one thread running, or at least be able to schedule tasks for execution in other threads, processes, CPUs, graphics cards etc.
A system is said to be concurrent ([concurrency]) if it can support two or more actions in progress at the same time. A system is said to be parallel if it can support two or more actions executing simultaneously.