A stress ball is a squeezable toy, usually not more than 6-8cm in diameter. It is squeezed and manipulated in the hand by the fingers, this is to either help relieve stress and muscle tension or to stretch and exercise the muscles of the hand.

There are many types of stress balls. Many are a closed cell foam rubber. Others contain gel of different densities, especially those balls used in physical therapy. Another type of stress ball uses a thin rubber membrane surrounding a fine powder. The latter type can be made at home by filling a balloon with baking soda. Some stress relieving balls are also used for promotional purposes.

Despite their name, many stress balls are not orb like or circular. Many stress toys or balls are moulded in interesting or funny shapes and printed with corporate logos. They are presented to employees and clients as gifts and marketing items.