With reference to descriptions of folds published by M. J. Fleuty in 1964 (for reference, see this Bibliography Vol. 30), development of precise terminology is discussed. Use of the term 'fold-envelope' (German = Faltenspiegel) is recommended. It is considered preferable to the term 'fold enveloping surface,' recently proposed by F. J. Turner and L. E. Weiss. Asymmetric folds are defined as those with alternately long and short limbs that have been developed in areas where fold axial planes are inclined to the fold-envelope. Rather than descriptive of the attitude of a fold in space, the term asymmetric fold should be used for the type of structure defined.