Floating ribs are four atypical ribs (two lowermost pairs, XI-XII) in the human

Human

Humans are the only living species in the Homo genus...

 ribcage. They are called so because they are attached to the vertebrae only, and not to the sternum or cartilage

Cartilage

Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...

 coming off of the sternum. Some people are missing one of the two pairs. Others have a third pair. Most, however, possess only two pairs.