What is the difference between Concurrency and Parallelism?

• Concurrency is when two or more tasks can start, run, and complete in overlapping time periods. It doesn’t necessarily mean they’ll ever both be running at the same instant. For example, multitasking on a single-core machine.
• Parallelism is when tasks literally run at the same time, e.g., on a multicore processor.

For instance a bartender is able to look after several customers while he can only prepare one beverage at a time. So he can provide concurrency without parallelism.