The term that describes an organism that can only exist as a group of cells is multicellular.

Here's why:

* Multicellular organisms are composed of more than one cell, with different cells specializing in different functions. They work together to form tissues, organs, and organ systems, creating a complex organism.

* Unicellular organisms, on the other hand, are made up of a single cell and can exist independently. Examples include bacteria, amoebas, and yeast.

So, if an organism cannot exist independently as a single cell but requires a group of cells to function, it is considered multicellular.