WAV is a kind of computer file that holds sound. You know one by the ending on its name: song.wav. Say it either as "wav" (rhyming with "have") or by spelling it out, W-A-V; both are normal, and "a WAV file" is the commonest way to say it.

What matters about WAV, next to MP3, is that it keeps everything. An MP3 throws away parts of the sound that most ears will not miss, so the file becomes small — good for phones and for sending. A WAV keeps the full recording, so it sounds as good as the original but the file is big; a few minutes of music can be tens of megabytes. Because of that, people who record and edit — musicians, sound engineers, anyone making a podcast — work in WAV, and only turn it into MP3 at the very end, for sharing.

The format came from Microsoft and IBM, so it has always been most at home on Windows; on Apple machines you will also meet AIFF, which does much the same job. You will hear WAV in ordinary talk too, whenever short sounds are involved: game sound effects, alert noises, ringtones.