Final answer:
Modern primates that habitually walk on two legs are called bipedal, a term that applies to humans who are the only existing primates to move bipedally as their primary means of locomotion.
Step-by-step explanation:
Modern primates that walk on two legs habitually are called bipedal primates. This mode of locomotion is unique to humans (Homo sapiens) within the primate group today. Other primates may walk on two legs occasionally, but only humans do this as their primary means of movement.
Bipedalism has allowed for a number of evolutionary changes, such as anatomical adaptations to balance the body on one leg at a time, which is necessary during the bipedal gait. Humans have continued to evolve from earlier human ancestors, known as australopithecines, who were also bipedal and set the stage for further evolutionary and cultural developments in hominids.
As bipedal primates, we share characteristics with other members of the order Primates such as larger brains, stereoscopic vision, and a trend toward holding the body upright.