In the computer world, what are OPUS files used for?

An OPUS file is simply an audio file created in the Opus format.

The Opus format is a lossy audio format developed for Internet streaming. Lossy file compression is a form of media compression that shrinks a file by discarding some of its information, creating a lower-fidelity approximation of the original file at a significantly smaller file size. The resulting audio may exhibit instances where the original information has been lost.

The Opus format uses codecs from both SILK (used by Skype) and CELT from Xiph.Org, a nonprofit organisation that produces free multimedia formats and software tools A codec compresses or decompresses media files such as songs or videos. The format supports variable bit rates from 6 kb/s to 510 kb/s. OPUS files are most commonly saved using the Ogg audio container format. For this reason, the files are sometimes referred to as Ogg Opus files. The Opus codec is used for Voice over IP (VoIP), video conferencing, and in-game chat. The format was standardised by and maintained by Xiph.Org.