Final answer:
A cohort is a collection of persons alive at a specified point in time who meet certain criteria, such as being born in the same period.
Step-by-step explanation:
A cohort is a collection of persons alive at a specified point in time who meet certain criteria, such as having been born during a particular time frame. This term is often used in demographic and social studies to examine patterns within a specific group. The correct answer to the question is 'a) Cohort', as it is defined as a group of people who share a statistical or demographic trait.
For example, the Baby Boomers are a well-known cohort consisting of individuals born between 1946 and 1964. Cohorts are critical for understanding population dynamics and for planning social services and economic strategies. Unlike a category or a generation, cohorts can provide insightful data due to their members experiencing similar social, cultural, and economic conditions throughout their lifespans.