It's a common expression used to express joy, happiness, or excitement. It can be used in various contexts, like:
* To express personal happiness: "¡Qué felicidad! Me gané la lotería." (What happiness! I won the lottery.)
* To react to someone else's good news: "Qué felicidad que te graduaste!" (How happy I am that you graduated!)
* To describe a situation: "Qué felicidad estar en la playa con el sol." (What happiness to be on the beach with the sun.)
It's a versatile phrase that can be used to convey a wide range of happy emotions!