AirTunes was announced in 2004, focused on playing audio wirelessly from iTunes to an AirPort Express. So you could listen to music all over your house from your mobile device.
In 2010, AirTunes became AirPlay to represent the extend scope of being able to play all kinds of content (including videos, photos, etc.).
So yes, there’s a difference (just audio vs all kinds of content).
Since AirTunes is the predecessor of AirPlay you can still use older hardware (like an old AirPort Express) in your network and mix them with new AirPlay hardware like an Apple TV (see screenshot). This means, that those AirTunes receivers still work like they should (you can send audio to them), although nowadays everyone talks about AirPlay.