Phenotypic switching (a.k.a. phenotypic dimorphism) is switching between two cell-types. An example is Candida albicans, which, when it infects host tissue, switches from the usual unicellular yeast-like form into an invasive, multicellular filamentous form. This switching between two cell-types is known as dimorphism.
Phenotypic switching in C. albicans include the switch from white cells to opaque cells in need for sexual mating.