The term "nerve" has several meanings, depending on its context.
1) In a general sense, it refers to courage or confidence in facing a difficult situation. For example, one might say "I had the nerve to ask her out."
2) It can also refer to a single strand of tissue that carries impulses between parts of the body along its length. These are called peripheral nerves and they connect the central nervous system (brain and spinal cord) with other organs, muscles, and sensory structures in the body.
3) In a more specific sense, "nerve" can refer to one of two large branches of the autonomic nervous system - the parasympathetic nerve or sympathetic nerve. These nerves control involuntary actions such as heart rate, digestion and respiration.
4) Finally, in a slang term, "nerve" can also refer to marijuana, specifically the resin glands on the plant's leaves that produce THC (tetrahydrocannabinol), which is the psychoactive component of the drug.