A coup d'état is a sudden, often illegal seizure of power from a government, typically executed by a small group, such as the military. In contrast, a revolution is a broader movement involving mass participation and aims to completely change the political or social system. While coups are often quick and elite-driven, revolutions tend to involve wide public support and grassroots mobilization. Coups can result in regime change without significant societal transformation, whereas revolutions typically entail profound changes in governance and social structures.