A jumping jack, also known as a star jump  and called a side-straddle hop in the US military, is a physical jumping exercise  performed by jumping to a position with the legs spread wide. The hands go overhead, sometimes in a clap, and then return to a position with the feet together and the arms at the sides.

Schoolchildren in the US performing jumping jacks.
The jumping jack exercise's origin has sometimes been erroneously identified as World War I U.S. General John J. "Black Jack" Pershing,[1] who is said to have developed it. The name comes from the jumping jack children's toy, which makes similar arm swing and leg splay motions when the strings are tugged.
Although he did not invent the exercise, the late fitness expert Jack LaLanne was credited for popularizing it in the United States. LaLanne used the jumping exercise during routines he promoted in decades of television fitness programming.[2]