Final answer:
The term used to describe the act of gathering to express views on public matters is 'demonstration,' a form of group-level political participation protected under free expression rights.
Step-by-step explanation:
The term used to describe the act of gathering together in order to express views on public matters is demonstration. This includes various forms of group-level political participation such as protests, assemblies, and public meetings. Demonstrations are a staple in democratic societies, enabling people to collectively participate in politics, demand government accountability, and call attention to various causes. The right to peaceful assembly is protected under rights to free expression, though subject to reasonable constraints to balance against public order.