![1boy 1girl black_hair blush bouncing_breasts breasts cattleya censored glasses greyscale hetero highres huge_breasts mature monochrome nipples penis ponytail queen's_blade satou_masa sex solo_focus sweat wide_hips rating:e score:0 post #216948](/cdn_image/preview/34/2e/342e0dad9f6222cf1b5076eb8f44d1c7.jpg)
Refers to breasts in motion, often as part of a .gif or flash animation. If it is not an animation, something like a motion blur or movement lines must be present to convey a sense of movement.
If one breast is up and the other is down, add the unaligned breasts tag as well.
Example: post #694780.
This tag implicates breasts (learn more).