Asklemmy

.wav files store volume levels (typically, but often higher) as a 16bit value 44100 times a second (again, typically, but often higher). This allows frequencies up to 22050Hz to be stored without losses. A lot of this is useless information, because most people don't hear anything above 16kHz, which only gets worse with age. Other parts of this might be useless information because of complex low frequency interaction with the inner ear which occlude some higher frequencies (psychoacoustics was a long time ago, can't explain it in detail). .ogg and .mp3 filetypes, among others, use that to simply cut frequencies that (probably) aren't heard. This process saves a lot of data, but results in lower resolution, especially in the higher frequencies (look up comparisons for 128kBit/s vs 320kBit/s MP3, you'll hear the difference immediately on pretty much anything other than phone speakers.)

If file size is an issue, .ogg is great, if quality is the most important, go for .flac, as flac files also don't loose any quality while having file sizes between the two, though compatibility might be a problem on older systems.