During the development of a multicellular organism, its cells specialise. what is this process of specialisation called?

Cellular differentiation is a process that exists in physiological, pathological and embryologic processes. In these processes a cell changes from one cell type to another. This process is related with the fact that somatic cells has the potential to grow and develop a multicellular organism, the development of an adult organism from a zygote is the result of cell division and differentiation