(November 2010) "Distilled Demographics," PRB's video series, highlights key demographic concepts such as fertility, mortality, and migration. Through these short videos, you can learn demography's real-world application and impact. "These videos not only show that demography can be exciting, but also highlight how population trends and issues affects the well-being of us all," says Carl Haub, senior demographer at PRB. "Fertility, mortality, and migration—along with other demographic issues—play a major role in determining what kind of opportunities and challenges people face in their communities and countries."

Migration is a minefield for demographers; varying definitions and measurements can be difficult to sort out. Migration is the geographic movement of people across boundaries to establish a new ­permanent or semipermanent residence. Along with fertility and mortality, migration is a component of population change. The terms "immigration" and "emigration" are used to refer to moves between countries (international migration). The parallel terms "in-migration" and "out-migration" are used for movement between areas within a country (internal migration).

How is an "immigrant" defined? Why do people migrate? How is the world becoming a "melting pot"? In this video, Haub answers these questions and clarifies how migration affects population.

We want to hear from you! Share your thoughts, impressions, and questions below. Have a question on world population and demography? Send in your question to Carl at askprb@prb.org.

PRB's Distilled Demographics video series is underwritten through the generosity of Juanita Tamayo Lott and Robert H. Lott in support of PRB's Millennial Generation Outreach Program, and in memory of Jorge del Pinal.