kappa

Kappa is a term that refers to several distinct concepts that share the same name. In the Greek alphabet, kappa (uppercase Κ, lowercase κ) is the tenth letter. Its name derives from the Phoenician letter koph and it is widely used as a symbol or variable in mathematics and the sciences.

In Japanese folklore, kappa is a water-dwelling imp or creature known as 河童. It is usually depicted as humanoid, greenish, and often with a hollow on its head that holds water, which keeps its power intact. Kappa are associated with rivers and ponds and are known for mischief; legends differ on whether they harm people or can be appeased through offerings, especially cucumbers, or friendly bows.

In statistics, kappa denotes measures of inter-rater agreement beyond chance. Cohen's kappa and Fleiss' kappa are widely used to assess reliability of categorical judgments, while weighted kappa is used for ordered categories. The term also appears in other contexts, such as the kappa distribution in probability theory.

In internet culture, Kappa is the name of a famous emote on the streaming platform Twitch, used to signal sarcasm or irony. The emote is an image of a former Justin.tv employee, Josh DeSeno, and has become a widely used shorthand in online commentary.