What is the "Foreshock", "Aftershock", and "Main Shock" of an earthquake?

What is the "Foreshock", "Aftershock", and "Main Shock" of an earthquake?

Tom Jordan (Director, Southern California Earthquake Center (SCEC)) gives expert video advice on: What is the probability of a severe earthquake striking a major city?; Where do earthquakes most often occur?; What are the most common earthquake myths? and more...

A foreshock is a small earthquake that occurs before a larger earthquake. Aftershocks are small earthquakes which occur following a larger earthquake. Main shock is a term that is used to distinguish a large earthquake from its foreshocks or its aftershocks.