An age cohort refers to

a. an aggregate of people born during the same time period.

b. the discrimination and prejudice toward a particular age group.

c. a type of age-based discrimination.

d. the hierarchical ranking of different age groups in society.

Age cohort is the group of people born during the same time. Due to their similar time of birth, they pass the course of life together. Therefore, the correct answer to your question is A. Example of the age cohort is the students of particular class, who are of same age group ad have similar expressions and concerns.