Here's why:

* Wave-like behavior: Light exhibits wave-like properties, such as diffraction and interference.

* Travels in straight lines: Light travels in straight lines in a uniform medium, a phenomenon known as rectilinear propagation.

* Fastest particle known: Light travels at the speed of light (approximately 299,792,458 meters per second in a vacuum), which is the fastest speed anything can travel in the universe according to our current understanding of physics. While light technically isn't a particle, it does have particle-like properties (photons) and behaves like a wave, making it the fastest thing we know of.

Important Note: The speed of light is constant, meaning it's the same for all observers regardless of their relative motion. This is a fundamental principle of special relativity.