Birthday by Katy Perry is a high-energy pop song that celebrates the joy and excitement of birthdays. The song's upbeat tempo and playful lyrics make it a perfect anthem for birthday celebrations. Key themes include celebration, fun, and making someone feel special on their big day. Perry uses a metaphorical approach to suggest that every day with a loved one feels like a birthday, emphasizing love, joy, and togetherness. Some poignant moments include the chorus, where she sings about blowing out the candles and making wishes come true, symbolizing the magical nature of birthdays and special occasions.