What term is used to describe organisms composed of identical and unspecialized cells?

Embryo cell or totipotent cell

Explanation:

All organisms during their embryonic stage also known as totipotent cells are composed of cells that are identical in structure and function. These cells can differentiate at a later stage and have the potential to become any cell i. e heart cell, eye cell etc. Embryo is thus just a mass of unspecialized cell which undergo differentiation to then convert into pluripotent and form tissues and hence the organ.