The abdomen, colloquially known as belly, tummy or tum, was an area of the humanoid body located under the chest. It contained the stomach.
When Blon Fel-Fotch Passameer-Day Slitheen, in the skin suit of Margaret Blaine, took Cathy Salt to the ladies toilets to kill her, she noted her "little tum" was "complaining" when she farted loudly. (TV: Boom Town)
Having been absorbed by the Abzorbaloff, Colin Skinner's face was embedded in the left side of the Abzorbaloff's abdomen. (TV: Love & Monsters)
Fiddling with an Adipose Industries pendant, Donna Noble inadvertently induced parthenogenesis in Stacy Campbell, causing her stomach to rumble as a newborn Adipose to protude from her abdomen. (TV: Partners in Crime)