The dura is the outermost of the three membranes that cover the brain and spinal cord. It is also the toughest and most fibrous of the three. Dura mater comes from the Latin for "hard mother."
We often see "dura" as part of other terms such as epidural, which means outside the dura. An epidural hematoma is an accumulation of blood outside the dura. Subdural means under the dura. A subdural hematoma is an accumulation of blood under the dura.