A succint explanation of concurrency vs. parallelism that I found online:

Concurrency is about dealing with lots of things at once. Parallelism is about doing lots of things at once. Not the same, but related. Concurrency is about structure, parallelism is about execution. Concurrency provides a way to structure a solution to solve a problem that may (but not necessarily) be parallelizable.

Source: https://talks.golang.org/2012/waza.slide#8