The spine is the connected column of bones running from the head to the lower back. A single bone is called a “vertebra and multiple bones are called “vertebrae”.
The spine has five sections. Each section is made up of a group of vertebrae.
The cervical (C) section is at the top of the spine (at the neck). There are 7 vertebrae in this section numbered top to bottom from C1 to C7.
Below the cervical section is the thoracic (T) section. There are 12 vertebrae numbered from T1 to T12.
The lumbar (L) section has 5 vertebrae numbered from L1 to L5.
The Sacral (S) section, also called the sacrum, have 5 vertebrae fused together as one bone.
At the bottom of the spine, 3 to 5 vertebrae are fused together as one bone segment in the coccygeal (Cx) section, also called the tailbone.
Source: https://msktc.org/sci/factsheets/Understanding_SCI_Part_1
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