Collective nouns are singular in form but can refer to multiple individuals or things. They are treated as singular nouns grammatically, taking singular verbs and pronouns. However, in certain cases, collective nouns can also be used in a plural sense when referring to the members of the group as separate entities. For example, "The team are training hard" (referring to individual team members) versus "The team is winning" (referring to the team as a unified group). The usage can vary depending on regional and contextual factors.