To put it simply, Cymatics is the study of sound and vibration made visible, typically on the surface of a plate, diaphragm or membrane. Every frequency exhibits a certain geometry, and patterns become more complex as frequency raises.
Why is this significant? Well, besides it being awesome, it has massive implications, and points to the fundamental structure of our universe. It provides evidence for the claim that all form in the physical world (including us) owes its existence to sound. Hence, Nikola Tesla's famous quote “if you want to find the secrets of the universe, think in terms of energy, frequency and vibration.”
You can research deeper if you're interested, but I'm just here to introduce topics and share some videos to help you get started. Below are cool demonstrations of patterns becoming more complex as frequency raises.
If you want to go down this rabbit hole, I recommend checking out the Ancient Knowledge series. It's like a compilation of videos organized to walk you through deep concepts. As with all research, "take it with a grain of salt". I don't personally resonate with every idea mentioned, and you don't have to either, but many scientific aspects are too interesting to pass up (for example, the universal mathematics presented in later parts). This is a great place to start exploring the topics of Consciousness, Cymatics and Sacred Geometry.