A collection of tissues that work together to perform a specific function is called an organ.

Here's a simple breakdown:

* Cells are the basic building blocks of life.

* Tissues are groups of similar cells that work together to perform a specific function (e.g., muscle tissue, nervous tissue).

* Organs are made up of different tissues working together to perform a more complex function (e.g., the heart, the stomach, the brain).

Let me know if you have any other questions!