Aflutter means in a state of excited, nervous movement or agitation, like the rapid flapping of wings. When your heart is aflutter before a big performance, it feels like butterflies are beating their wings inside your chest. When flags are aflutter in a strong breeze, they're flapping and rippling energetically.

The word captures both physical fluttering and that jittery, anticipatory feeling you get when something important is about to happen. A classroom might be aflutter with excitement on the last day before winter break, with students barely able to sit still. A neighborhood could be aflutter with activity as everyone prepares for a street festival.

The “flutter” part comes from the quick, light movements of bird wings or insect wings. Think of how a hummingbird's wings move so fast they're almost a blur. When you're aflutter, you have that same kind of restless, vibrating energy. You might feel aflutter before meeting someone you admire, or when you're waiting to hear whether you made the team. It's that fizzy, can't-quite-hold-still sensation that comes with nervous excitement.