A fidget spinner is a toy that consists of a ball bearing in the center of a multi-lobed (typically two or three) flat structure made from metal or plastic designed to spin along its axis with little effort. Fidget spinners became popular toys in April 2017, although similar devices had been invented as early as 1993. 

The toy has been promoted as helping people who have trouble focusing or those who fidget to relieve nervous energy, anxiety, or psychological stress. There are claims that a fidget spinner can help calm down people who have anxiety and other neurological disorders like ADHD and autism. However, as of May 2017, there is no scientific evidence that they are effective as a treatment for autism or ADHD.
(Source: Wikipedia)