VoiceOver, when referring to iPods, stands for the text to speech system built in to the iPod shuffle, iOS (for iPod Touches), and 5th thru 7th Generation iPod nanos. Apple's VoiceOver system is usually used just by those with disabilities who require text to speech functionality (those who are vision impaired/blind or those with dyslexia). But on devices like the iPod shuffle, VoiceOver was designed to be used by all users.
In the iPod shuffle, VoiceOver helps listeners navigate music playback by speaking the titles of songs and playlists. VoiceOver was implemented in the 3rd and 4th generation iPod shuffle.
Wikipedia Entry on VoiceOver: https://en.wikipedia.org/wiki/VoiceOver
Apple Support page for VoiceOver on iPods: https://support.apple.com/en-us/HT202024
iPod Shuffle 3rd Generation VoiceOver guide (archived): https://web.archive.org/web/20140223074230/http://support.apple.com/kb/HT3475
iPod Nano 5th Generation VoiceOver guide (archived): https://web.archive.org/web/20141230235000/https://support.apple.com/en-us/HT3870