The parenchyma is the functional parts of an organ in the body (i.e. the nephrons of the kidney, the alveoli of the lungs). This is in contrast to the stroma, which refers to the supporting tissue.
In plants, parenchyma are unspecialized, thin-walled cells that make up the bulk of most nonwoody structures. Parenchyma cells in between the epidermis and pericycle in a root or shoot constitute the cortex, and are used for storage of food. Parenchyma cells within the center of the root or shoot constitute the pith. There are three types of parenchyma: leukoplast for storage of starch, chromoplast for color pigment, and chloroplast for holding chlorophyll.