A collective noun is a word like company, team, government, family and so on, which is singular in form but collective in sense.
In British English, however, verbal agreement may be either singular or plural. Thus, The committee is/are not agreed; the family is/are..., depending on whether the writer/speaker has in mind the group as a sole entity or several members of the group.
Variations on the theme include words like media, which are plural in form, but are sometimes, despite many people considering such usage incorrect, used with singular verbs: "The media has shown great interest in these events."
 See also