Bushy-tailed describes someone who is energetic, eager, and full of enthusiasm, especially early in the morning or at the start of something new. The phrase comes from how a squirrel's tail looks when the animal is alert and active: fluffy, upright, and ready for action.

When your teacher arrives at school bright-eyed and bushy-tailed on Monday morning, she's awake, cheerful, and ready to teach, even if some students are still rubbing sleep from their eyes. A new employee might show up bushy-tailed on their first day, excited to learn and make a good impression.

The phrase usually includes “bright-eyed” before it, creating the full expression bright-eyed and bushy-tailed. While it suggests admirable energy and readiness, people sometimes use it with gentle humor to describe someone who seems too enthusiastic when others are tired. If your friend bounds into your tent at summer camp at 6 a.m., cheerfully suggesting a hike, you might groan and mutter that nobody should be that bushy-tailed before breakfast.