semant

Async in JavaScript refers to asynchronous programming, which is a model that allows multiple things to happen at the same time. In JavaScript, async functions return a promise of nothing, and the async keyword is placed before a function to identify it as asynchronous.

Concurrency in C refers to concurrent execution, which is when multiple tasks are executed at the same time but not necessarily simultaneously. Concurrency can be achieved through multithreading, which is when different threads are doing different things at the same time.

Therefore, the main difference between async in JavaScript and concurrency in C is that async is a programming model, whereas concurrency is a type of execution. Async is about the way functions are executed, while concurrency is about how multiple tasks are handled.