Especially popular in the 1980s and 1990s in the United States, and regaining popularity in the mid-2010s, a scrunchie is a loop of elastic typically around 1-3" in diameter (around 2-8 cm), with a shirred or otherwise loosely crumpled - indeed, scrunched - layer of soft fabric covering the elastic and fully enclosing it so that it does not directly touch anything the scrunchie is wrapped around.
Scrunchies are primarily intended for use as ponytail holders, especially for naturally curly hair and hair which is very thick and long. They serve this purpose more gently than a hair elastic made of exposed rubber (or even a regular rubber band), causing less breakage to individual strands of hair, and less friction when removing them, making them more comfortable and less potentially painful to remove. They also generally have a wider overall diameter in order to accommodate greater volume and thickness of hair than the strength of a narrower hair elastic can manage.
Scrunchies may be worn on the wrist as an accessory (or simply as temporary storage for a scrunchie that is not currently in use, but may be wanted later). Scrunchies are generally perceived as highly informal and highly feminine tools for dressing one's hair or accessorising; men with long hair are more likely to use plain elastics to secure their hair. It would be unusual to see a scrunchie worn in a professional or formal setting; doing so is likely to be considered inappropriately cutesy for the context, as it is a very dated fashion trend associated with teenage girls.
Iron Noder 2018, 25/30