The term MASS OF CELLS can be described as a honeycomb, which is a structure made up of nine letters. A honeycomb is a structure composed of many small hexagonal cells that are connected together to form a larger structure. It is often used in architecture and engineering, as well as in nature, where it is found in the nests of bees and other insects. The structure of a honeycomb is strong and efficient, making it an ideal material for many applications.