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 by relieving nervous energy or psychological stress. There are claims that a fidget spinner can help calm people down who suffer from 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.  
The popularity of the toy among children and teenagers led some schools to ban the spinners from class for being a distraction, while other schools have allowed the toy to be used discreetly.
Fidget spinners are toys not unlike yo-yo or other skill toys, designed to spin with little effort.   A basic fidget spinner consists of a two- or three-pronged design with a bearing in its center circular pad.   A person holds the center pad while the toy spins.  They are made from various materials including brass, stainless steel, titanium, copper, aluminium, and plastic.   The bearings are generally ceramic, metal (stainless steel or chrome), and some are hybrids—such as ceramic balls with stainless races and cages. Each fidget spinner also has two or more weights on the outside that make it spin faster and stay balanced. Bearings can vary to adjust for the design's spin time, vibration, and noise, causing unique sensory feedback.
Being a kind of a flywheel of a gyroscope in principle, fidget spinners come with similar effects enabling a player to pull various tricks and stunts while forces of a gyroscope take hold. A fidget spinner can be balanced on top of fingers, thrown and caught, and so on. 
As of 2017, the patent status of the various fidget spinners on the market was unclear. 
Catherine Hettinger, a chemical engineer by training, was initially credited by some news stories to have been the inventor of the fidget spinner, including by media outlets such as The Guardian,  The New York Times,  and the New York Post.  Hettinger filed a patent application for a "spinning toy"  in 1993 and a patent was issued, but Hettinger allowed the patent to lapse in 2005 after she could not find a commercial partner.   A May 2017 Bloomberg News article showed that Hettinger was not the inventor of the fidget spinner, and Hettinger agreed. 
In an interview appearing on May 4, 2017 on NPR, Scott McCoskery described how he invented a metal spinning device in 2014 to cope with his own fidgeting in IT meetings and conference calls.  In response to requests from an online community, he began selling the device he called the Torqbar online. 
Marketing and sales
With the rapid increase in the spinner's popularity in 2017, many children and teenagers began using it in school, and some schools also reported that kids were trading and selling the spinner toys.   
As a result of their frequent use by schoolchildren, many school districts banned the toy.   Some teachers argued that the spinners distracted students from their schoolwork.  According to a survey conducted by Alexi Roy and published in May 2017, 32% of the largest 200 American public and private high schools had banned spinners on campus. 
When fidget spinners rose in popularity in 2017, many publications in the popular press discussed the marketing claims made about them for people with ADHD, autism, or anxiety.    However, there is no scientific evidence that fidget spinners are effective as a treatment for children with autism or ADHD.