Australopithecus afarensis, commonly known as "Lucy" is one of the most important hominid fossils. This fossil kind, has long arms, and small brain capacity like modern apes. But the most significant feature of them was their bipedal movement style. There are more than 300 individuals of this kind dated between 4 and 3 million years ago. They all have the same characteristic pelvis bone that proves bipedal walking. Also their footprints proved that they walked as modern homos.
Naming of fossils are very problematic. Because, Australopithecus took its name when it was first found. That means "monkey of the south". But the researchers did not know that this kind had the ability to walk on their two leg when they gave this name to them. If they recognized that feature, they would give "Homo erectus" to Afarensis, I believe. Because the Homo erectus has its name because of its recognized bipedal walking ability.
As far as I know, A. afarensis is one of our ancestors, I don't care what we call them. It's more important to understand them.