Definition for Mosaic
From Biology Forums Dictionary
1) An individual in which some cells throughout the body show genetic differences. For example, in female mammals, about half of the somatic cells will express one X-linked allele, while the rest of the somatic cells will express the other allele.
2) Individuals have been identified who have two different karyotypes, such as 45,X/46,XY or 45,X/46,XX.