Variable geometry refers to systems or structures that can change their shape or configuration to adapt to different conditions or requirements. This concept is often applied in engineering and design, allowing for flexibility and efficiency in various applications, such as in aircraft wings or mechanical systems. In the context of international relations, variable geometry describes arrangements where some countries participate in certain agreements or initiatives while others do not. This approach allows for tailored cooperation among nations, accommodating diverse interests and capabilities, as seen in organizations like the European Union or NATO.