means A synthetic elastic fabric, prized for its ability to stretch far beyond its resting size and snap back, used in athletic wear, swimwear, and form-fitting clothing.

from Spandex is an anagram of "expands" — a rare case of a word literally rearranged from what it does, coined in the mid-20th century by chemists who developed the polyurethane-based fiber. In Europe it often goes by "elastane," and the DuPont brand name "Lycra" became so famous it nearly swallowed the generic term whole.