[b]"Concurrency vs Parallelism: What's the Real Difference and When to Use Each?"[/b] Alternatively, if you prefer a

Short answer: Concurrency = multitasking, parallelism = multicore.

Web servers? Concurrency (async/await) for I/O-bound stuff. Parallelism for heavy math (think NumPy with OpenMP).

Gotcha: Debugging parallel code is *painful*. Use `thread sanitizers` or `rayon` in Rust to save your sanity.