Definition of "variegation"

The variegation of leaves occurs so commonly that we do not often inquire into the cause of it. To the physiologist, however, the question of the origin of variegation is of considerable importance, and it certainly is not less so to the horticulturist, whether pleasure or profit be the main end of his endeavors.

1878, The Eclectic Magazine of Foreign Literature, Science, and Art, volume 27, page 509

The second and related type of white variegation is formed by the formation of a single loose layer of short palisade cells instead of a compact layer or two of long palisade cells in the green sectors of variegated leaves (La Rocca et al. 2011).

2014, Ulrich Lüttge, Wolfram Beyschlag, Progress in Botany, Springer, page 244