Modifications of a given musical theme. Variation form is a structural organization in which a theme is presented and then followed by the modified versions of the original theme. An abbreviation for an entry in the works catalog of Carl Phillipp Emanuel Bach by Wotquenne; H. numbers, based on Helm's newer catalog, have superceded the W. numbers (which are now given in parentheses following the H. numbers).
A musical form in which a theme is presented then repeated many times in different guises created by the transformation of elements such as rhythm, tempo, harmony, and accompaniment.
Optional rules agreed on before beginning a game, e.g., Plunge, Sevens, Splash, etc. (Some say "indicating" and the Nel-O option in a forced bid are variations to basic 42.)