An aggregation of cells and extracellular material which performs a discrete function is called a tissue.

Here's why:

* Cells: Tissues are composed of cells, which are the basic unit of life.

* Extracellular Material: This includes the non-living components surrounding the cells, such as the extracellular matrix (ECM). The ECM provides structural support, helps regulate cell behavior, and acts as a medium for communication between cells.

* Discrete Function: Tissues are specialized to perform a particular function within an organism. For example, muscle tissue contracts to produce movement, while nervous tissue transmits signals.

Let me know if you'd like to learn more about specific types of tissues!