What are the last two pairs of ribs commonly referred to as?

The last two pairs of ribs are commonly referred to as floating ribs. This is because they do not attach to the sternum or to the costal cartilage of other ribs, which is a distinguishing feature of these specific ribs. Instead, their posterior ends are attached to the vertebrae, while the anterior ends remain free, hence the term "floating." Floating ribs typically are the 11th and 12th pairs of ribs in the human rib cage and are important in providing protection to the kidneys and other organs in the lower torso, while also allowing for some flexibility in the lower part of the ribcage.