An example of an output device that interfaces between computers and humans is:

A speaker serves as an output device that converts digital signals from a computer into sound waves that humans can perceive. This allows users to receive auditory information from the computer, which is essential for applications such as music playback, notifications, and other audio outputs. Speakers specifically communicate the output from the computer to the user, engaging the auditory sense, which is a fundamental aspect of human-computer interaction.

The other options present devices that primarily serve different roles: a keyboard is an input device used for typing information into the computer, while a mouse is also an input device that helps users navigate and interact with the computer interface. A printer, while it does produce output, primarily generates a physical copy of digital documents, and thus operates in a different context than audio output. The focus here is on how a speaker effectively fulfills the role of an output device by providing a direct method for humans to receive information from the computer audibly.