the size of the intervertebral foramen becomes narrower during normal flexion movement.

Vertebral foramen are the spaces between adjacent vertebrae where the spinal nerves exit the spinal canal.

vertebrae

Inter means "between", vertebral obviously means vertebrae as mentioned above, and foramina is plural for foramen, which is a hole.

Intervertebral foramina are formed in the space between two vertebrae. When two or more vertebral bones are stacked, the intervertebral foramina would be inferior to the pedicles of the superior vertebrae and superior to the pedicles of the inferior vertebrae. It will create a hole that goes between the two vertebrae horizontally. The spinal cord goes through the vertebral foramen vertically, and the nerve roots slip out horizontally through the intervertebral foramina.

Spinal cord passes through the vertebral foramen of vertebrae C1-C7, T1-T12 and L1 (sometimes L2).

Cauda equina (nerve roots of lower spinal cord) pass through the vertebral foramen of vertebrae L3-L5 and the sacral canal.

Spinal nerve roots pass through all of the intervertebral foramen and the sacral foramen.