Groups of different types of tissues working together are referred to as organs.

Here's why:

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

* Organs: Structures composed of different tissues that work together for a common purpose (e.g., the heart, lungs, stomach).

For example, the heart is an organ composed of muscle tissue (to pump blood), nervous tissue (to regulate heartbeat), connective tissue (to provide structure), and epithelial tissue (to line the chambers).