Population growth

Population growth is the rate at which a population grows or expands. For example, if a population increased from 100 to 110 in a year, then it would have had a population growth of 10% per year.
World population.
World population has been rising since the end of the Black Death, around the year 1350. 
Population began growing rapidly in the Western world during the industrial revolution. Several factors were notable: the coming of modern agriculture, and the control of epidemic diseases (black death, cholera, typhus). Modern water engineering brought clean water to many large cities. Deaths from world wars, especially WWI, reversed the trend, but only for a while. 
The most significant increase in the world's population has been since the 1950s in Asia and Latin America. Medical advances, and increases in farming, have been the main causes.
A single example is both astonishing and revealing. Since 1945, half the forests of Indonesia have been replaced with farmland. As late as 1900, Indonesia was still a densely forested country: forests covered 84 percent of the total land area. Deforestation became serious in the 1970s, and has gone faster since then. About 170 million hectares (estimated in 1900) decreased to less than 100 million hectares by the end of the 20th century. In 2008, it was estimated that tropical rainforests in Indonesia would be logged out in a decade. Of the total logging in Indonesia, up to 80% is said to be done illegally.