C#: What is the difference between async and parallel?

1// Async
2var task1 = HttpClient.GetAsync(url1);
3var task2 = HttpClient.GetAsync(url2);
4await Task.WhenAll(task1, task2);
5
6// Parallel
7Parallel.For(0, 100, i =>
8{
9    HeavyComputation(i);
10});