There are many ways to divide the electromagnetic spectrum, and there isn't one universally agreed-upon set of four major regions. However, here are four regions that are often considered major and cover a wide range of the spectrum:

1. Radio Waves: The longest wavelengths, ranging from millimeters to kilometers. Used for communications, broadcasting, radar, and medical imaging.

2. Infrared Radiation: Wavelengths between visible light and microwaves. Important for heat transfer, used in thermal imaging, remote sensing, and communication.

3. Visible Light: The narrow band of electromagnetic radiation that our eyes can see, responsible for our perception of color.

4. Ultraviolet Radiation: Wavelengths shorter than visible light. Has high energy and can be harmful, but also used for sterilization, medical imaging, and tanning.

It's important to note that there are other regions of the spectrum beyond these four, including:

* Microwaves: Used for cooking, communications, and radar.

* X-rays: Used in medical imaging and materials science.

* Gamma rays: The highest energy radiation, used in medical treatment and astronomy.

The specific breakdown of the spectrum can vary depending on the context and the purpose of the classification.