Both groups and cohorts are collections of students. However, there are several differences between them. We can sum up these differences in one sentence, that is, cohorts enable administrators to enroll and unenroll students en masse, whereas groups enable teachers to manage students during a class. So, you can think of a cohort as a collection of students who are staying together in order to complete an entire course or sequence of courses together. Groups are smaller sets of students within the course.
Here's another way to approach it: Think of a cohort as a group of students working together through the same academic curriculum; for example, a group of students all enrolled in the same course. Think of a group as a subset of students enrolled in a course. Groups are used to manage various activities within a course.
Cohort is a system-wide or course category-wide set of students.
There is a small amount of overlap between what you can do with a cohort and a group...