Succinctly, breasts in a tight sweater.
Also, sweater muffins, sweater meat, sweater puppies, etc.
One of the many names internet people call breasts; you are unlikely to encounter this term outside the internet and if you use it outside the internet you are less likely to be understood.
A lame neologism. There are better words for breasts.
Exempli gratia:
Bombshells, Gazingas, Milk Fountains, Milk Shakes, Molehills, Spheres of Venus, Knockers, Mommas, Globes, Mondos,the Twins, Boobies, Montezumas, Gongas, the girls, Moo Moos, and Sweater Stuffers.