The document discusses key concepts relating to population including: - Population is defined as the number of people living in one place and can be classified by gender, age, place of work, and other factors. - Birth rate is the number of babies born in a period of time while death rate is the number of people who die, and their difference is the natural growth rate. - Migration refers to people moving to live in a different country, with immigrants moving to live in a new country and emigrants leaving their existing country. - Population density refers to whether an area is densely or sparsely populated.