When something "Resonates" it creates a full, harmonious, meaningful sound or experience. For example, a person can "resonate" with another person if they enjoy each others company. A sound can "resonate" with your ears if you think that sound is beautiful or perfect. A sound can also resonate with a room if you feel the acoustics in that room are perfectly reflecting the sound. In a sentence, when something resonates, it connects with something in a perfect way, like a harmony between two musical notes or an excellent relationship between two people.

1. To exhibit or produce resonance or resonant effects. 2. To evoke a feeling of shared emotion or belief: "It is a demonology [that] seems to resonate among secular and religious voters alike" 3. To correspond closely or harmoniously: "Symbolism matters, especially if the symbols resonate with the larger message"

When something resonates, it will vibrate or echo in harmony. In the context of the song from Evanescence, the singer is saying that two people are in sync with one another, and that they move as one, breathe as one, and think as one. It's a very romantic sentiment, and used often in songs, poems, and stories about true love. Typically, resonate is a word most commonly used in science, for example when talking about frequencies. You might also be familiar with resonance as part of the long form name of an MRI- magnetic resonance imager, a medical scanner. In new age spiritualism, resonance is used to describe the harmony of energy flows in the human body, and some people believe that crystals can help balance the resonances within your body's energy lines.