Imagine a tiny ring made of metal that can be split in half so it looks like a little "C" shape. This is what we call a split-ring resonator (SRR) and it is too small to see with your own eyes.
Resonator means it can vibrate back and forth in a certain way when energy (like light or electricity) is sent to it. The way it vibrates can change depending on how big the split is in the ring, and how the ring is shaped.
Scientists and engineers use SRRs to control electromagnetic waves, which are invisible waves of energy that travel through the air. They use them to create things like tiny antennas, radar, and even cloaking devices (to hide objects from being seen by certain electromagnetic waves).
But in simpler terms, a split-ring resonator is like a small magic ring that can help scientists and engineers control and manipulate invisible energy waves.