What is Opus?

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. Royalty-free, equally good on speech and music, and usually wrapped in an Ogg container. It always runs at 48kHz internally.

What is WAV?

Uncompressed audio, roughly 10MB a minute, and the format every piece of audio software will accept without complaint. Nothing is compressed and nothing is lost, which makes it the right thing to edit and the wrong thing to email.