Your body maintains an energy reserve in its fat cells as a part of normal operating procedure, but sometimes fat cells grow where they shouldn't. This results in fatty deposits, also called lipomas, and although some may find them gross, they're almost always harmless.
Fatty deposits are small, round masses of fat cells below your skin, between your skin and muscle. These lumps feel kind of soft, and maybe doughy or rubbery, and if you poke at one you'll notice it moves around (go ahead; they're usually painless). Lumps usually don't grow larger than a few centimeters (about half an inch), and most often grow on the neck, shoulders, arms, upper back, upper thighs and buttocks [source: WebMD, Salam].