Can I host a Minecraft server from an iPad/iPod?

Under normal conditions, you simply can't. You can't use the Desktop version of Minecraft on iPad because you can't run the Java files on iPad. A non-jailbroken iPad will never allow Java to run like that.

Some people are trying to get this to work with jailbroken iPads which can run java. It's still not working, and only an iPad 3 would yield remotely acceptable performance for a low-end server. I strongly recommend against trying unless you're doing this as a "because I can" project.

If you mean for Minecraft Pocket Edition, you can just play locally with other MPE players over Wifi. It's really easy, but it's not a "Minecraft Server" in the same sense and Desktop players won't be able to access your "server".

So far, a minecraft server has been utilized on an iPad 3, sporting the 1GB of RAM. The server boots up but the moment it gets to the portforward step, it fails. So far, nobody has been able to port forward on an iOS device. This progress was achieved on a jailbroken iPad 3, running the iFile, JavaVM, and Mobileterminal plugins available via Cydia.

On an ASUS Transformer android tablet however, a low level, vanilla minecraft server has been hosted and confirmed to work. Ports are forwarded, and local computers on the ASUS Transformer's internet connection can connect. The device is able to host the server in creative mode, with no mobs, and connect 2 people.

But to answer your question, Apple has made it so that this cannot be done. Well, not until we find out how to forward ports on a iOS device, such as the iPad 3.