Hominin: all the species belonging to the human lineage. This includes modern humans, extinct human species, and all our immediate ancestors (including members of the genera Homo, Australopithecus, Paranthropus, and Ardipithecus. 

Hominid: the group of all modern and extinct Great Apes (e.g. modern humans, chimpanzees, gorillas, and orangutans, plus all their immediate ancestors).

Bipedalism is the main trait that separates hominins from all other hominids.

You must be familiar with the following species involved in human phylogeny:

• Australopithecus afarensis

• Paranthropus sp.

• Homo habilis

• H. erectus

• H.heidelbergensis

• H. neanderthalensis

• H. sapiens

• H.floresiensis

• Denisovans

Hominins include living humans, our ancestors (pre-humans) and the bipedal apes with whom we share our evolutionary history. 

About 6-7 mya, the ancestor of living humans and chimpanzees diverged into two geographically isolated populations. One of those groups eventually evolved into us, the other evolved into chimps. Thus, we and the living chimps share a common evolutionary ancestor who lived about 6-7 mya in Africa. This is demonstrated by the fact that we share about 99% of our DNA. 

The most defining characteristics of hominins is our bipedal (two footed) locomotion and upright posture. It is a form of locomotion found 6-7 Mya. The earliest hominins also show changes in tooth form that mark a change in diet and social organisation.

Dozens of hominin species lived on earth. Most of the evidence on hominin lineage is from fossils and as more and more fossils are found; the hominin lineage is refined.