Also known as: 乳揺れ, あばれる乳, おっぱいぷるんぷるん, 荒ぶるおっぱい, アニぱい, 乳揺れ(うごイラ), 乳分身, 乳摇
Breasts in motion, usually in an animation. If it is not an animation, something like a Motion Blur or Motion Lines must be present to convey a sense of movement.
If the breasts are bouncing in opposite directions, add the Unaligned Breasts tag as well.