It can be compared to individual or pair work.
Example
Learners in threes, a class separated into two, and an open class, are all examples of groups.
In the classroom
Group work increases the opportunities for all learners to speak the new language, it allows them to learn from each other, and frees the teacher to monitor individuals and give them feedback. Examples of typical group work activities include ranking discussions, jigsaw activities, project work group and group writing tasks.
Further links:
https://www.teachingenglish.org.uk/article/freeze-writing-a-way-make-writing-tasks-a-group-activity
https://www.teachingenglish.org.uk/article/working-pairs-groups
https://www.teachingenglish.org.uk/article/group-discussion-skills