Axis vertebra is characterized by presence of deltoid ridge/odontoid process.

Explanation

### Step-by-Step Solution:

1. **Identify the Axis Vertebra**: The axis vertebra is the second cervical vertebra in the human spine, also known as C2.

2. **Characteristic Features**: The axis vertebra is specifically characterized by the presence of the odontoid process, also known as the dens. This is a bony projection that extends upward from the body of the axis.

3. **Distinguish Between Terms**: It is important to note that the term "deltoid ridge" refers to a different anatomical feature. The deltoid ridge is a triangular area located on the humerus (the bone of the upper arm) and is not associated with the axis vertebra.

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