parallelism vs concurrency

From the Java Threads and the Concurrency Utilities book that i am reading on Safari:

I thought this was a good explanation

parallelism is “a condition that arises when at least two threads are executing simultaneously.” In contrast, concurrency is “a condition that exists when at least two threads are making progress. [It is a] more generalized form of parallelism that can include time-slicing as a form of virtual parallelism.”