A cohort is a group of people who share something important in common, usually an experience or a time period.

In school, your cohort might be everyone in your grade who started kindergarten the same year you did. You all move through school together, facing similar challenges at similar times. Scientists studying how children learn might track a cohort of students from first grade through high school, observing how the group changes over time.

In ancient Rome, a cohort was a unit of soldiers who trained and fought together. Today, we still use it for groups connected by shared experiences. A company might hire a cohort of new employees who all start on the same day and go through training together. Researchers studying aging might follow a cohort of people born in 1950 to see how their generation's health changes over decades.

What makes a cohort different from just any group? The members typically share a specific starting point or defining characteristic that shapes their experience. Your soccer team is a group, but all the students who entered your school district in 2019 form a cohort. The shared timeline or experience matters because it means the cohort faces similar circumstances that might affect everyone in comparable ways.