The ability of stem cells to cross the barrier of differentiation to transform into a cell of another lineage expressing the molecular characteristics of different cell type with the ability to perform the function of the new cell type is referred as:
Transdifferentiation is defined as:-

The change of a cell or tissue from one differentiated state to another.
The differentiation of a tissue-specific stem cell into another type of cell as for example a bone marrow stem cell differentiating into a neuron.

Dedifferentiation

It is a cellular process commonly believed to be uniquely available to lower life forms such as worms and amphibians in which a partially or terminally differentiated cell reverts to an earlier developmental stage.
Cells in cell culture can lose properties they originally had such as protein expression or change shape. This process is also termed dedifferentiation.
Dedifferentiation can also be observed in some tumour e.g. dedifferentiated liposarcomas which will show more immature areas in an otherwise differentiated liposarcoma.
Regression of a specialized cell or tissue to a simpler, more embryonic, unspecialized form i.e. a reversal of cell development so that differentiation that had occurred previously is lost and the cells become more generalized in structure.

Redifferentiation

A process by which a group of once differentiated cells return to their original specialized form.
De differentiation
Re differentiation
Trans differentiation
Sub differentiation