A tremor is a trembling or shaking in a person or the Earth. If you're scared about speaking in public you might have a tremor in your voice — or wish that an earthquake tremor would open up the floor and swallow you first.
If you're nervous or feeling queasy as you read a paper aloud, you might get a tremor in your hands and the paper itself will start to shake. When an earthquake rumbles, a powerful tremor might make a building shake so that it looks as fragile as a piece of paper. Not every tremor comes from fear or seismic activity, though: you can tremor or quiver with excitement as you anticipate something enjoyable.