It's often used for cases made of leather or fabric, but can also be applied to other materials like metal or plastic.
Here are some examples of how "etui" can be used:
* "He gifted her a beautiful leather etui for her new pen."
* "She kept her glasses in a stylish etui when not in use."
* "The vintage etui for the cigarette lighter was a collector's item."
In essence, an étui is a small and elegant container designed to protect and enhance the object it holds.