group action; collective behavior; collective behaviour; acting as a group
leading group (of runners in a marathon, etc.); leading pack
living in a group; communal living; community life
group suicide; mass suicide; arranged suicide of two or more people
going to school in groups
mass infection; infection outbreak; infection cluster
gang assault; mob violence; gang rape
class action; class-action suit; class-action lawsuit
mass outbreak (of a disease)
employment en masse (esp. of middle and high school graduates from the rural districts during Japan's post-war economic boom)
group medical examination
collectivism (giving priority to a group rather than any individual member)
social group with common ties to a region
consanguineous group; kin group
gang stalker; mass stalker; gang stalking; mass stalking
occupational group; professional group; occupational cohort
crime whose goal requires a large number of people acting together (e.g. insurrection)