What is NSwag "client"?

I'm a Java tester and I've been moved to C# team. I was going to help my team with an integration backend testing. They use NSwag for generation "clients" and use it in tests. The problem for me is to understand what exactly it is that "client". I understand a client as e.g. browser which calls requests to server. What does "a client" mean regarding NSwag? Can anyone help and try to explain that to me as much simple as you can?