A foramen is an opening in a bone or organ.
The foramen ovale for example is found in the heart. It allows blood to communicate between the atria in the foetus but is intended to close shortly after birth.
In a long bone (such as the femur), the foramen enables blood vessels carrying oxygen to the blood cells to pass through.
Several foramina are therefore found in the bones of the skull.
« Foramina » is the traditional pleural form (Latin) although the term "foramens " is also used.
A picture of the occipital bone of the cranium The foramen magnum can be seen in the middle (10) © aj gazmen, Flickr, CC BY-NC-ND 2.0