In the practice of medicine, especially surgery and dentistry, anesthesia is an induced, temporary state with one or more of the following characteristics: analgesia (relief from or prevention of pain), paralysis (extreme muscle relaxation), amnesia (loss of memory), and unconsciousness.
An anesthetic is an agent that causes anesthesia.
A patient under the effects of anesthesia is anesthetized.
An anesthesiologist (US) or anaesthetist (UK) is a physician who performs anesthesia.
A Certified Registered Nurse Anesthetist is an advanced practice nurse who performs anesthesia.

Anesthesia enables the painless performance of medical procedures that would cause severe or intolerable pain to an unanesthetized patient.

Three broad categories of anesthesia exist:
- General anesthesia suppresses central nervous system activity and results in unconsciousness and total lack of sensation.
- Sedation (or dissociative anesthesia) inhibits transmission of nerve impulses between the cerebral cortex and limbic system, which inhibits both anxiety and creation of long-term memories.
- Conduction anesthesia, commonly known as regional or local anesthesia, blocks transmission of nerve impulses between a targeted part of the body and the spinal cord, which causes loss of sensation in the targeted body part. A patient under conduction anesthesia remains fully conscious. Two categories of regional anesthesia exist. A peripheral blockade inhibits sensory perception in a body part, such as numbing a tooth for dental work or administering a nerve block to stop sensation from an entire limb. A central blockade (epidural and spinal anesthesia) administers the anesthetic around the spinal cord, which suppresses all sensation below the block.

Adapted from Wikipedia, the free encyclopedia. Internet. Accessed on May 17, 2016.