Wiffleball is a baseball variant designed for indoor play and play in confined areas. It is played using a plastic perforated ball and a long, plastic (typically yellow) bat. While The Wiffle Ball, Inc., manufacturer of the plastic ball has developed a set of rules for the game, actual implementations tend to vary from backyard to backyard. Generally it is played on a triangular playing field and unlike baseball, does not require the running of bases. Instead, runner placement and advancement is determined by the distance the ball is hit. The official rules from The Wiffle Ball, Inc. were included in the ball's packaging until the 1960's.

The Wiffleball was invented by David N. Mullany of Shelton, Connecticut in 1953 as he attempted to design a ball that would curve easily for his 12-year old son, and was named when his son and his friends would refer to a strikeout as a "whiff" at the perforated plastic ball. A classic wiffleball is about the same size as a regulation baseball (smaller "mini" balls and larger "softball" sizes are also available) and is hollow plastic no more than 1/8th of an inch thick. One hemisphere is perforated with eight 3/4" inch oblong holes, with the other hemisphere solid. By throwing the ball so it rotates on its axis with its equator on the seam between the two hemispheres, the ball will typically move counter to the direction of the perforated hemisphere (although the ball has been known to move erratically as well with different rotation). Every Wiffleball box is printed with instructions on how to throw a curveball and a slider.

Wiffleballs are typically packaged with a plastic yellow bat that measures 30 inches in length and about 1.5 inches in diameter and like the ball, is hollow. The original bat was made of wood and the yellow bat made today is maufactured by a company other than The Wiffle Ball, Inc. Today, a variety of bats made of varying materials including wood and aluminum are specifically manufactured for Wiffleball.

Wiffleball has had an immense popularity since its inception. From 1956 to 1992, The Wiffle Ball, Inc. often promoted their product alongside pictures of baseball stars like Ted Williams and Pete Rose. After discontinuing these advertisments due to cost, the company found little or no difference in sales. Today the game has undergone an explosion of popularity, with many successful leagues and tournaments across the United States. Some tournaments in New England have been known to draw more than 100 teams that typically consist of 2-5 people each.