Table 1:

Definition of key terms used in this review.

Term	Definition
Perivascular space	The compartment surrounding (from the Ancient Greek: peri – around) a brain or spinal cord blood vessel, that is, arteries, arterioles, venules, and veins, and located within the parenchyma This is not necessarily a fluid space but could also be filled with extracellular matrix.
Periarterial and perivenous space	The perivascular space surrounding an artery or vein, respectively.
‘Paravascular’ space	From the Ancient Greek para (next to), the non-concentric compartment alongside blood vessels in the subarachnoid or subpial space on the surface of brain and spinal cord, as recently visualized during intravital microscopy.
Virchow-Robin space	Large perivascular spaces that are visible macroscopically or on magnetic resonance imaging (MRI).
Glia limitans	Formed by compacted astrocyte foot processes and an overlying parenchymal basement membrane