Final answer:
The number of live births per year for every 1000 people in the population is referred to as the birth rate, which is crucial for demographic studies.
Step-by-step explanation:
The concept that refers to the number of live births per year for every 1000 people in the population is known as the birth rate. Sociologists use this measure, also called the crude birthrate, to assess and understand fertility within a population. The birth rate provides valuable insights into population growth when analyzed alongside the mortality rate, which is a measure of the number of people who die per year per 1000 people.