Final answer:
Sovereignty is the supreme and absolute authority a state has within its territorial boundaries, allowing it to govern itself and manage its affairs independently.
Step-by-step explanation:
The supreme and absolute authority within territorial boundaries is known as sovereignty. This concept implies that a sovereign state governs itself independently, without interference from other states, and has full authority over its internal and external affairs, including the right to make war, peace, treaties, or alliances. The notion of sovereignty is a key element in the European international system, indicating that all states are equal in status and should respect each other's sovereignty by not interfering in domestic affairs.
However, this also leads to an anarchical international system where states must be prepared to defend themselves, often leading to increased insecurity and conflict. In contrast, in a unitary system of government, the central government holds most of the power, while in a federal system, two levels of government exist, both granted authority by the constitution.