Grinding (also called freaking or freak dancing) is a dance where two or more people rub or bump their bodies against one another. It became popular in night clubs. The dance then moved into high schools across the United States and Canada.
Schools have tried to ban grinding because it is very sexual.
A dance similar to grinding is "The Bump", which was popular in the 1970s. Another is the twerk, which became popular through the 2000s into the 2010s.