Interface (noun)

1. A point where two systems, subjects, organizations, etc. meet and interact, typically creating a boundary.
2. A surface forming a common boundary between two adjacent regions, spaces, materials, etc.
3. An interface between computer hardware and software that enables the user to interact with a computer.

Origin:

Late 19th century: from french interface, from inter- "between" + face "face".

Examples:

1. The interface between the two systems was seamless, allowing for easy integration.
2. The interface between the lake and the ocean was gradual and not easily distinguishable.
3. The interface of the new software was intuitive and user-friendly.
4. The interface between the different parts of the device was well designed.
5. The interface between the computer and the printer was easy to install and use.