Before you wonder what a class looks like in C#, you should know that you've been working with a class this whole chapter. By default, every script created in Unity is a class, which you can see from the class keyword on line 5:
public class LearningCurve: MonoBehavior
MonoBehavior just means that this class can be attached to a GameObject in the Unity scene. In C#, classes can exist on their own, which we'll see when we create standalone classes in Chapter 5, Working with Classes and Object-Oriented Programming.
The terms script and class are sometimes used interchangeably in Unity resources. For consistency, I'll be referring to C# files as scripts if they're attached to GameObjects and as classes if they are standalone.