What is the definition or description of: lumbar puncture?

See below: A lumbar puncture is a medical procedure where a sample of fluid is taken from inside the lower back for testing. A hollow needle is inserted between two bones, called vertebrae, at the base of the spine and is used to draw fluid out. A lumbar puncture is most commonly carried out when it's thought that a condition such as meningitis has developed inside the brain or nervous system.

Obtain spinal fluid: To test for meningitis or multiple sclerosis or a variety of problems, a small needle is inserted into the lumbosacral cistern to obtain spinal fluid for testing and perhaps diagnostic confirmation.