Wiktionary
n. A class of board game very similar to chess but with variant rules and pieces
Wikipedia
Fairy chess comprises chess problems that differ from classical (also called orthodox) chess problems in that they are not direct mates. The term was introduced by Henry Tate in 1914 and has resisted change since then. While selfmate dates from the Middle Ages, helpmate was invented by Max Lange in the late 19th century. Thomas Dawson (1889–1951), the "father of fairy chess", invented many fairy pieces and new conditions. He was also problem editor of Fairy Chess Review (1930–51).
Although the term "fairy chess" is sometimes used for games, it is more usually applied to problems where the board, pieces, or rules are changed to express an idea or theme impossible in orthochess.
Usage examples of "fairy chess".
We're playing fairy chess in five dimensions, and she's teaching me songs you taught her.
As Heckle's living read-head ingested and interpreted the coded candybytes, the raven jumped around the table like a fairy chess knight, a corvine Turing Train.
Louis and Teela were out on the lawn, soaking up sunshine and playing a deadly serious game of fairy chess.