Using comma in inheritance: is it multiple inheritance?

I’m quite new to C# and there’s something I don’t understand. I thought multiple inheritance wasn’t possible in C#.

However, I’m using classes that seem to use multiple inheritance, in particular to use Event System.

public class Slot : MonoBehaviour, IPointerClickHandler
{
    #region IPointerClickHandler implementation
    public void OnPointerClick(PointerEventData eventData)
    {
           //Do some stuff here...
    }
    #endregion
}

If it’s not multiple inheritance, then what is it?

It is not multiple inheritance. It is using interfaces. It can always only inherrit one class (MonoBehaviour in your example). It can also implement any number of interfaces alongside that (Usually they can be recognised by the I in front of their name, IPointerClickHandler in your case).

An interface is basically something that tells you that your class has this mothod/property (OnPointerClick in your example). It doesn’t tell you how this method/property is implemented. Each class that implements an interface has to do this for himself.