Migration!

The term migration came up in class today. Here is a definition that I found online:

Human migration is physical movement by humans from one area to another, sometimes over long distances or in large groups. The movement of populations in modern times has continued under the form of both voluntary migration within one's region, country, or beyond, and involuntary migration (which includes the slave trade, Human traffic in human beings and ethnic cleansing). People who migrate are called migrants or more specifically, emigrants, immigrants, or settlers, depending on historical setting, circumstances and perspective.

What are your comments? Is there anything that you don't agree with in this definition? Are you confused? Give me feedback...