What's the difference between Observable and Observer patterns in .NET C#?

Does anyone know the difference between the two? and what would be the use for each one?

>Solution :

Observer: Any object that wishes to be notified when the state of another object changes.

Observable: Any object whose state may be of interest, and in whom another object may register an interest.

https://www.infoworld.com/article/2077258/observer-and-observable.html