Axis is the name for:
Second cervical vertebra (axis)

Presence of odontoid process.
Transverse processes are small and lack the anterior tubercle.
Anterior margin of the inferior surface of the body projects downwards to a considerable extent.
Foramen transversarium is directed superolaterally (expand in typical vertebrae it is directed vertically)
Inferior surface presents a deep and wide inferior vertebral notch placed in front of the inferior articular process. The superior vertebral notch is shallow and is present behind the superior articular process.

Key concept:
Second cervical vertebra is called the axis. it is identiﬁed by the presence of the dens or odontoid process which is a strong, tooth-like process projecting upwards from the body. The dens is usually  believed to represent the centrum or body of the atlas which has fused with the centrum of the axis.
IV cervical vertebra
III cervical vertebra
II cervical vertebra
I cervical vertebra