Chimera
An animal chimera is a single organism that is composed of two or more different populations of genetically distinct cells that originated from different zygotes involved in sexual reproduction. Chimeras are formed from at least four parent cells (two fertilized eggs or early embryos fused together). Each population of cells keeps its own character and the resulting organism is a mixture of tissues.
Regarding mosiac: If the different cells have emerged from the same zygote, the organism is called a mosaic.