sorry to have to ask, but I don't know what this term means, and can't find a simple definition.
I want to know if I need to enable this in order to users to use their iphone client that I am writing to register a brand new account with my openfire server.
Thanks!
In-band registration means that users that do not have an account on your server can register one using the XMPP protocol itself, so the registration stays "in band", inside the same protocol you're already using. That's opposed to doing the registration out-of-band, for example by having to go to a website to sign up and then returning to the XMPP client software. XMPP specifies the in-band method of registration in XEP-0077 and many XMPP clients support it.