1: Redifferentiation is the process by which the de-differentiated cells (meristems/ tissues which were able to divide and produce new cells) lose their dividing ability and start getting differentiated and specialised.
2: Products of redifferentiation in dicots
Fully differentiated permanent parenchymatous cells get dedifferentiated into meristematic cells of interfascicular cambium and cork cambium. These cambial cells then keep on dividing during secondary growth. Finally, they get re-differentiated giving rise to secondary xylem, secondary phloem, secondary cortex (phelloderm) and cork (phellem).
3: Tumour
Tumour is an undifferentiated mass of cells. It is formed by cell division of cells which were already differentiated and have undergone the process of dedifferentiation and regained the ability of cell division.