"Subtle vibration" refers to a very gentle or light movement or shaking that is difficult to notice or perceive.
Sentences with «subtle vibration»
Your watch will send subtle vibrations through your wrist, helping you time out your breath so it is long and slow, reducing your heart rate. (canadianbusiness.com)
Never miss important calls and messages again with custom alerts on your ring using subtle vibration patterns and light. (geekwrapped.com)
These signatures are neutrinos (subatomic particles that stream out of a collapsing star's center) and gravitational waves (subtle vibrations of spacetime that will also ripple out from the convulsing star). (sciencenews.org)