Concurrency is a system-structuring mechanism, parallelism is a resource. (ref)
There's an important distinction between "parallelism" as a resource, and "parallel execution". The two are often confused, but they are in fact distinct. The key separator is "concurrency":
no parallelism | has parallelism | |
---|---|---|
no concurrency | sequential execution | sequential execution † |
has concurrency | concurrent execution ‡ | parallel execution |