Noticeably means in a way that's easy to see, hear, or detect. When something changes noticeably, the difference is clear enough that people will spot it without having to look closely. If your friend gets a haircut and it's noticeably shorter, you'll see the difference right away. If someone speaks noticeably louder after you ask them to repeat themselves, the volume increase is obvious.

The word often appears when describing changes or differences. After practicing piano all summer, you might play noticeably better when school starts. Your little brother might grow noticeably taller over the course of a year. A room becomes noticeably quieter when everyone stops talking at once.

Sometimes people use this word to be diplomatic when pointing out something awkward: “She was noticeably absent from the meeting” suggests everyone wondered where she was. The word highlights that the thing being described isn't subtle or hidden. It's right there for anyone paying attention to observe.