It is often used in scientific and technical contexts to indicate the presence of four of something.
Here are some examples:
* Tetracycline: An antibiotic with four rings in its chemical structure.
* Tetrad: A group of four. For example, in biology, a tetrad refers to four chromatids formed during meiosis.
* Tetrahedron: A geometric shape with four faces, four vertices, and six edges.
* Tetralogy: A set of four related works of art, such as a group of four novels.
So, whenever you see "tetra" as a prefix, you can usually assume it signifies something that has four parts or components.