What properties must a group of cells have to name these tissue cells?

A multicellular organism differs from a unicellular organism both in that it consists of a large number of cells and in the fact that its cells are differentiated. They are distinguished by their structure and function. In primitive multicellular organisms, although different cells are different, they do not lie in groups, but mixed, therefore they cannot be called tissues.

Tissue is a group of cells that have the same origin, structure and perform a similar function. In animal tissues, the intercellular substance is a mandatory component.