What is OGG?
Ogg Vorbis is the patent-free lossy format that came out of the free software world. It compresses well and it has always been unencumbered, which is why games, Wikipedia and open-source projects reach for it while consumer hardware mostly ignores it.
What is OPUS?
Opus is the best-sounding lossy codec at low bitrates by a comfortable margin, which is why it carries the audio in nearly every voice and video call you make. It is royalty-free, it handles speech and music equally well, and it is usually wrapped in an Ogg container.