Genetics is the study of heredity, the process by which characters are passed on from parents to their offsprings, so that their offspring show resemblance with each other and with the parents. But no two offspring are identical. They differ from each other and also from their parents in some respects.
Genetics tries to explain the mechanism and the basis for similarities and differences between related individuals. These two aspects are respectively called heredity and variation. Heredity is the process of transmission of characters in living beings from parents to offspring. It also called inheritance.