The cerebral cortex is the outer layer of the cerebrum of the brain and also covers the cerebellum. It's about 2-4 mm thick and consists of six separate layers. It's almost entirely made up of neurons. It plays a major role in memory, attention, awareness, thought, language, and consciousness.
Because it takes on a grey color when preserved, the cortex is usually referred to as "grey matter", even though in a living brain it has no distinct color.
In large mammals, particularly humans, the cortex is intricately folded to provide it with more surface area. It's believed that this characteristic is a key feature in establishing mammalian intelligence.
The parietal lobe, temporal lobe, occipital lobe, and frontal lobe are all structures of the cortex.