We recently introduced Misrepair-accumulation theory as an interpretation on aging mechanism. For better understanding this theory, we discuss here in more details the new concept of Misrepair and the concept of accumulation of Misrepairs. I. Aging takes place uniquely on the systems that have a well-defined structure: an organization of its sub-structures. Aging of a non-living system is a result of accumulation of injuries (damage) of its structure. II. A generalized concept of Misrepair is important for reaching to a unified understanding of aging changes. In the situation of a severe injury, incorrect repair is a repair essential for maintaining structural integrity for increasing the surviving chance of an organism. With the same mechanism as that in "Misrepair of DNA" , the term of "Misrepair" can be used for describing all kinds of incorrect repairs on different types of living structures, including molecules, cells and tissues. A new concept of Misrepair is therefore proposed and defined as incorrect reconstruction of an injured living structure. Misrepair mechanism is beneficial for the survival of an organism, and it is essential for the survival of a species. III. Alteration of structure made by Misrepair is irreversible; therefore Misrepairs accumulate and disorganize gradually a structure, which appears as aging of it. Accumulation of Misrepairs takes place on molecular, cellular and tissue levels respectively: on tissue level, it appears as disorganization of cells and extracellular matrixes (ECMs); on cellular level, it appears as deformation of cytoskeleton and change of cell shape; and on DNA, it appears as accumulation of DNA mutations and alteration of DNA sequence. An essential change in aging of an organism is an irreversible change of the spatial relationship between cells/ECMs in a tissue. In conclusion, aging of an organism is a result of accumulation of Misrepairs on tissue level.