A Jibber Jabber is someone who talks, but makes absolutely no sense. They never seem to realise that no one knows what they are saying, so carry on regardless. You can usually spot a Jibber Jabber by the person they are talking to. They generally look extremely confused and their eyebrows are pushed deep over their eyes in a bid to take some sort of information from the interaction.
Jibber Jabber: Jibber jabber jibber jabber square jibber jabber jibber jabber quadratic jibber jabber jibber jabber year 10.
Confused party: Err, I don't know, Err.
Jibber Jabber: Jibber jabber jibber jabber 7.15 jibber jabber.
Confused party: Mate, I have no clue what you are talking about!