Crude birth rate indicates the number of live births occurring during a year per every 1,000 people in a given population in a given year.

The “Green Revolution” is the name given to a series of technological innovations in the 1940s, 50s, and early 60s that led to a massive growth in agricultural production around the world in the late 1960s. This led to massive population growth, particularly in the developing world.

The “natural increase rate” is a statistic used to measure the growth of population in a region, exclusive of immigration and emigration. It only considers the crude birth rate and the crude death rate. If the death rate is higher than the birth rate, then the region has a “negative natural increase rate.”

The total fertility rate is the average number of children born to each woman in a given region during the course of her lifetime. Anything higher than four is a very high total fertility rate and anything lower than two is a very low total fertility rate. Most of the developed world is fairly close to two and much of the developing world is close to, or in excess of, four.

The maternal mortality rate reflects the number of women, per thousand, who die during childbirth. So, if the maternal mortality rate is high (like in Sierra Leone or Bangladesh) then the number of women who die during childbirth is high. To provide possible clarification, “maternal” means motherly and “mortality” means death.

The "baby boom" generation began in 1946, the year after the end of the Second World War, and lasted until 1964. This generation is primarily unique to the United States, although other Western countries experienced a similar spike in birth rate and lowering of the death rate. The baby boom generation began when the millions of soldiers returned home from war and were offered unprecedented job opportunities and access to higher education. Marriage rates and fertility rates both rose as the population skyrocketed.

Although gender is a relevant factor in determining life expectancy in the United States, it is far less variable than race. While in general women have a life expectancy of two or three years more than men, the difference between life expectencies of white people and black people in the United States can be as much as ten years. There is a number of reasons why this is, including black people being much more likely to experience violence and receive poor healthcare; however, the primary reason is that institutional racism remains a part of American society and white Americans are much more likely to be wealthy.

Maternal mortality rate refers to the number of mothers who die in childbirth for every thousand births. The infant mortality rate refers to the number of babies who die before their first birthday for every thousand births. In countries where both these numbers are high (like South Asia or Sub-Saharan Africa), the total fertility rate is also likely to be high. The total fertility rate reflects the number of children who are born on average to a woman during her lifetime. In societies where a large proportion of children die young, the total fertility rate is likely to be much higher than in countries where the vast majority of children survive to adulthood.

The period from 1964 to around 1980 is often called the “Baby Bust.” This is because the total fertility rate declined significantly from the era of the “Baby Boom” generation. The total fertility rate declined for many different reasons, but the primary reason was the relatively dramatic increase in female empowerment during this time period. More women were university-educated, more were entering the workforce, more were using contraception, and more were waiting longer to have children. The cumulative effect was a decline in the natural increase rate and the total fertility rate.

Improved healthcare can have conflicting and widely variable influences on the rate of population growth. It rather depends on the starting point from which you are improving. For example, in South Sudan, increased access to medicine and better prenatal care would lead to a rapid growth in population in a short space of time; however, in Germany, improved healthcare would provide contraception and family planning advice, which would lead to a declining rate of population growth.