Gram.
a noun, as herd, jury, or clergy, that appears singular in formal shape but denotes a group of persons or objects.
[ 1510-20 ]
Usage . Whether a COLLECTIVE NOUN, which is singular in form, is used with a singular or plural verb depends on whether the word is referring to the group as a unit or to its members as individuals. In American English, a COLLECTIVE NOUN naming an organization regarded as a unit is usually treated as singular: The corporation is holding its annual meeting. The team is having a winning season. The government has taken action. In British English, such nouns are commonly treated as plurals: The corporation are holding their annual meeting. The team are playing well. The government are in agreement.
When a COLLECTIVE NOUN naming a group of persons is treated as singular, it is referred to by the relative pronoun that or which: His crew is one that (or which ) works hard. When such a noun is treated as plural, the pronoun is who: His crew are specialists who volunteered for the project. In formal speech and writing, COLLECTIVE NOUNS are usually not treated as both singular and plural in the same sentence: The enemy is fortifying its (not their ) position. The enemy are bringing up their heavy artillery.
When the COLLECTIVE NOUNS couple and pair refer to people, they are usually treated as plurals: The newly married couple have found a house near good transportation. The pair are busy furnishing their new home. The COLLECTIVE NOUN number, when preceded by a, is treated as a plural: A number of solutions were suggested. When preceded by the, it is treated as a singular: The number of solutions offered was astounding.
Other common COLLECTIVE NOUNS are class, crowd, flock, panel, committee, group, audience, staff, and family.