Here's why:

* Electromagnetic Radiation: Gamma rays are a form of electromagnetic radiation, like visible light, radio waves, and X-rays.

* Electric and Magnetic Fields: Electromagnetic radiation consists of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation.

* Transverse Waves: A transverse wave is one where the oscillations are perpendicular to the direction of wave travel. Since the electric and magnetic fields in gamma rays oscillate perpendicular to the direction of wave propagation, they are considered transverse waves.

In summary: The electric and magnetic fields that make up gamma rays oscillate perpendicular to the direction of wave travel, making them transverse waves.