第15页 1.9.1

We use the term concurrency to refer to the general concept of a system with
multiple, simultaneous activities, and the term parallelism to refer to the use of
concurrency to make a system run faster.

页码是中文版页码，对应中文在1.9.1第一段。中文翻译没什么问题。
无论是中文还是原文，每个字我都懂，但我还是不懂concurrency 和parallelism 的区别是什么……
球指点