Midriff is a particular term to denominate the section of the human body between the thorax

Human rib cage

-See also:*Terms for bones*Terms for anatomical location*Articulation of head of rib-References:* Clinically Oriented Anatomy, 4th ed. Keith L. Moore and Robert F. Dalley. pp. 62–64...

/chest

Chest

The chest is a part of the anatomy of humans and various other animals. It is sometimes referred to as the thorax or the bosom.-Chest anatomy - Humans and other hominids:...

 and the pelvis/hips

HIPS

HIPS may refer to:* High impact polystyrene* Home Information Pack* Host-based intrusion-prevention system, a computer security system oriented towards workstations...

. It is used (1) as a genteel avoidance of synonymous belly

Abdomen

In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

(with its primary external physical feature, the navel

Navel

The navel is a scar on the abdomen caused when the umbilical cord is removed from a newborn baby...

); (2) as a synonym for waist

Waist

The waist is the part of the abdomen between the rib cage and hips. On proportionate people, the waist is the narrowest part of the torso....

; and (3) as a name for the area around (yet mainly below) the diaphragm

Thoracic diaphragm

In the anatomy of mammals, the thoracic diaphragm, or simply the diaphragm , is a sheet of internal skeletal muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity from the abdominal cavity and performs an important function in respiration...

 (particularly including the stomach

Stomach

The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...

 region).

The midriff is exposed when wearing a crop top

Crop top

A crop top is a T-shirt or blouse with the lower part cut off, showing of some of the abdomen. The half shirt is a kind of shirt that is cut off from the bottom of the chest....

 or bikini

Bikini

The bikini is typically a women's two-piece swimsuit. One part of the attire covers the breasts and the other part covers the crotch and part of or the entire buttocks, leaving an uncovered area between the two. Merriam–Webster describes the bikini as "a woman's scanty two-piece bathing suit" or "a...

.