Do multicellular organisms differ from unicellur organisms?

A colonial organism is a collection of one-celled organisms living together.

The difference between a multicellular organism and a colonial organism is that individual organisms from a colony can, if separated, survive on their own, while cells from a multicellular life-form (e.g., cells from a brain) cannot.

Multicellular organisms consist of differentiated cells that perform special tasks. The entire organism requires all the different types of cells to be present, and the individual cells can not survive without being in the organism