Concurrency means executing multiple tasks at the same time but not necessarily simultaneously. For example, suppose you have two chores to complete. Make a sandwich and clean your room. Preheating the Sandwich maker is a good place to start, and while it’s heating up, you can finish making your bed.
Return to the kitchen and butter both sides of the bread, then add your favorite vegetables and place it in the sandwich maker to grill. You can finish cleaning your room while this is going on, which is an example of concurrency.
In concurrency, system resources are switched backed and forth between the tasks but both the tasks aren’t computed simultaneously.
Parallelism means that application tasks can be processed in parallel, for instance on multiple CPUs at the exact same time. In our example, you can ask your brother to make the sandwich and you can finish cleaning the room which is an example of parallel processing. You have multiple core CPUs on your laptop which can be leveraged if you have a CPU-intensive task.
Node js Workers threads or WEB workers are used for parallel computing. In conclusion, Concurrency is about dealing with lots of things at once. Parallelism is about doing lots of things at once