When someone is perky, they seem confident, happy, and ready to move. They sit up, smile, talk in a lively way — not drooping, not tired. It is informal, a little cute, and not for serious reports. People say it of children, small animals, and of someone who has just cheered up. You also hear perk up: to become more awake or more cheerful. People stretch the same idea to things that stand up in a lively way — a hat, a plant, a tail. They sometimes use it about a body that looks firm and sits up; that use is informal and can feel personal. The core picture does not change: up, bright, not slack. It is not a compliment you would put in a job reference; it is everyday talk, and it can sound slightly teasing if the cheer feels like a performance.