Plant variegation is when parts of a plant's leaves turn white. Normally, the plants will get more variegated when placed in the bright sun.
Variegation is a result of cell mutation. The lack of green color on the plant's leaves makes it harder for the plant to grow since it is not able to absorb as much chlorophyll as a normal green plant.
To be able to propagate a plant that is variegated, one must take a cutting from the plant that has variegated leaves. If you only take a totally green shoot from an otherwise variegated plant, the shoot will not grow to be variegated.
Variegation in plants is often sought after due to its uniqueness. Many green enthusiasts collect plants with many variegations. Most often the variegation of a plant is white, but there are also yellow and pink variegation.