The "Three Pound Brain" refers to the average weight of the human brain, which is approximately three pounds (1.4 kilograms). This organ is responsible for controlling all bodily functions, processing sensory information, and enabling cognitive abilities such as thinking, memory, and decision-making. The brain is composed of various regions, each with specific functions, including the cerebrum, cerebellum, and brainstem. The brain's complexity is highlighted by its approximately 86 billion neurons and trillions of synapses that facilitate communication within the nervous system. Understanding the brain's structure and function is crucial for fields like neuroscience and psychology, as it helps researchers explore how the brain influences behavior and mental health.