Bubbly, loud, and enthusiastic, ebullience means "the quality of being cheerful and full of energy." Take a room full of seven-year-olds and add a bunch of adorable puppies, and you'll end up with ebullience.
The Latin word ebullientem, which ebullience comes from, literally means "boiling over." When you see ebullience, you know it; it's not simply happiness or enjoyment, but those emotions bubbling up and overflowing.