The cylinder of parenchyma tissue found in the centre of plant stems to the inside of the vascular tissue. It is light in weight and has been put to various commercial uses, notably the manufacture of pith helmets.

2. (not in scientific usage) The white tissue below the rind of many citrus fruits.

3. To destroy the central nervous system of an animal, especially a laboratory animal such as a frog, by severing its spinal cord.