乳揺れ 荒ぶるおっぱい アニぱい 乳揺れ(うごイラ) 乳分身 あばれる乳
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.
This tag implicates breasts (learn more).